The 100 most-cited articles in Physical review. B./Physical review. B, 2022

Many-body localization (MBL) is a mechanism by which quantum chains with strong enough disorder can avoid thermalization. Here, the authors define and locate several distinct landmarks having to do with thermalization, rare many-body resonances, and so-called thermal avalanches in systems that can exhibit MBL. These landmarks are well separated in the strength of the disorder, and the estimate of where MBL breaks down in asymptotically large systems is far beyond what is usually pointed to as the MBL transition.

Tailoring optical nonlinear effects (e.g., harmonic generation, sum-frequency mixing, etc.) in the recently emerging all-dielectric platform is important for both fundamental science and industrial development of high-efficiency, ultrafast, and miniaturized photonic devices. In this paper, we propose a method for the dynamically switchable high-harmonic generation in silicon nanodimer metasurfaces by exploiting the polarization-controlled dual bound states in the continuum (BIC). Owing to the high-quality factor of BIC resonances, efficient harmonic signals including the third-harmonic generation and fifth-harmonic generation from a direct process as well as a cascaded process by degenerate four-wave mixing are obtained. Moreover, the BIC and their resonantly enhanced harmonics can be switched on or off with high selectivity with respect to the fundamental pump polarization. Compared with previous reports, our paper provides a simple but effective tuning strategy by fully exploring the structural symmetry and polarization degree of freedom rather than resorting to additional…

Quantum anomalous valley Hall effect (QAVHE), which combines both the features of QAHE and AVHE, is both fundamentally intriguing and practically appealing, but is experimentally challenging to realize in two-dimensional (2D) intrinsic magnetic materials to date. Here, based on first-principles calculations with the density functional theory $+U$ approach, we predicted the electronic correlation-driven valley-dependent quantum phase transition from ferrovalley (FV) to half-valley-semiconductor (HVS) to QAVHE to HVS to FV phase in single-layer RuClBr. Remarkably, the QAVHE phase with an integer Chern number ($C=1$) and chiral spin-valley locking, which is induced by sign-reversible Berry curvature or band inversion between ${d}_{xy}/{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals, can achieve complete spin and valley polarizations for low-dissipation electronics devices. We also find that the electron valley polarization can be switched by reversing magnetization direction, providing a route of magnetic control of the valley degree of freedom. An effective…

Using the linear response-based constrained local density approximation (cLDA) approach we systematically computed the Hubbard $U$ parameters for series of $3d, 4d,$ and $5d$ transition metals. We compare the results with estimations by the constrained random phase approximation (cRPA) method and discuss the performance of the self-consistent density functional theory + $U$ ($\mathrm{DFT}+U$) method for prediction of lattice parameters, work functions, $d$-bandwidths and $d$-band centers. Interestingly, we found that blindly applied the standard, fully localized limit (FLL) version of the $\mathrm{DFT}+U$ approach heavily overestimates the positions of $d$-band centers with respect to the Fermi level, but much better agreement with experiment is obtained when applying a more realistic, Wannier-type representation of $d$ orbitals for projection of $d$ states occupancies. We present another, independent estimate of the Hubbard $U$ parameter based on the comparison of Hartree-Fock and DFT eigenvalues, and positions of $d$-band centers. The so-derived estimates are surprisingly well…

Phonon anharmonicity is critical for accurately predicting the material's thermal conductivity ($\ensuremath{\kappa}$). However, its calculation based on the perturbation theory is a difficult and time-consuming task, especially for the high-order phonon scattering process. In this work, using cubic boron arsenide (BAs) and diamond as examples, we combine the machine learning potential (MLP) with molecular dynamics simulations to predict $\phantom{\rule{4pt}{0ex}}\ensuremath{\kappa}$ and assess the effect of anharmonicity on thermal transport properties. A MLP based on the matrix tensor algorithm is developed in this work, which can accurately describe lattice dynamics behaviors in both BAs and diamond. The phonon spectral energy density analysis reveals that MLP can effectively capture both the phonon mode softening and the linewidth broadening induced by the anharmonicity at finite temperatures in both materials. Compared to diamond, BAs exhibits a stronger anharmonicity revealed by the larger deviation from equilibrium position and more pronounced phonon broadening effect,…

Entanglement is a key tool to classify quantum phases of matter in and out of equilibrium. Here, the authors introduce a phenomenological quasiparticle picture for entanglement dynamics in monitored systems evolving under the effect of quantum jumps. Within this picture, entanglement is carried by non-Hermitian quasiparticles, associated to the no-click limit of the measurement protocol, that propagate ballistically and are randomly reset with a rate given by their inverse lifetime. The authors show how this picture qualitatively reproduces the entanglement transition in the monitored Ising chain.

Many-body localization (MBL) freezes the dynamics of a disordered quantum interacting system, inhibiting thermalization and resulting in a persistent memory of the initial state. Here, with the help of extensive numerical simulations, the authors find slow decay of the imbalance, a quantity often employed in experimental studies of MBL, even though the disorder strength considerably exceeds the current estimates of the position of the MBL transition. This suggests a slow approach to thermal equilibrium and identifies challenges for unequivocal numerical and experimental demonstrations of MBL.

We investigate the charging process of quantum battery (QB) systems in an extended Dicke model with both atomic interactions and an external driving field. We focus on the effects of the atomic interaction and the external driving field on the charging performance of the QB and find that the maximum stored energy of the QB has a critical phenomenon. We analyze the critical behavior and obtain the analytical expression of the critical atomic interaction. The dependence of the maximum stored energy, the energy quantum fluctuations, and the maximum charging power on the number $N$ of the two-level systems are also discussed. In particular, for the maximum charging power, we obtain the quantum advantage of the QB, which approximately satisfies a superlinear scaling relation ${P}_{\text{max}}\ensuremath{\propto}{N}^{\ensuremath{\alpha}}$, where scaling exponent $\ensuremath{\alpha}$ varies with the number $N$ of the two-level systems. In the ultrastrong coupling regime, the atomic interaction can lead to faster battery charging, and the quantum advantage $\ensuremath{\alpha}=1.88$ can be…

Over a decade of work has culminated in the consensus that one-dimensional systems, subject to sufficiently large disorder, fail to thermalize and possess an extensive set of local integrals of motion. In this Letter, I will provide numerical evidence for the contrary. In particular, this work studies the dynamics of disordered spin chains which are weakly coupled to a Markovian bath. Within this approach, the critical disorder for stability to quantum avalanches exceeds ${W}^{*}\ensuremath{\gtrsim}20$ in the random field Heisenberg chain. In stark contrast to the Anderson insulator, the avalanche threshold drifts considerably with system size, with no evidence of saturation in the studied regime.

$\mathrm{SCAN}+\mathrm{rVV}10$ has been demonstrated to be a versatile van der Waals (vdW) density functional that delivers good predictions of both energetic and structural properties for many types of bonding. Recently, the ${\mathrm{r}}^{2}\mathrm{SCAN}$ functional was devised as a revised form of SCAN with improved numerical stability. In this work, we refit the rVV10 functional to optimize the ${\mathrm{r}}^{2}\mathrm{SCAN}+\mathrm{rVV}10$ vdW density functional and test its performance for molecular interactions and layered materials. Our molecular tests demonstrate that ${\mathrm{r}}^{2}\mathrm{SCAN}+\mathrm{rVV}10$ outperforms its predecessor $\mathrm{SCAN}+\mathrm{rVV}10$ in both efficiency (numerical stability) and accuracy. This good performance is also found in lattice-constant predictions. In comparison with benchmark results from higher-level theories or experiments, ${\mathrm{r}}^{2}\mathrm{SCAN}+\mathrm{rVV}10$ yields excellent interlayer binding energies and phonon dispersions for layered materials.

Two-dimensional ferrovalley semiconductors with robust room-temperature ferromagnetism and sizable valley polarization hold great prospects for future miniature information storage devices. As a new member of the ferroic family, however, such ferrovalley materials have rarely been reported. By first-principles calculations, we identify that monolayer $\mathrm{Ce}{\mathrm{I}}_{\text{2}}$ is an intrinsic ferromagnetic semiconductor and exhibits excellent ambient stability, strong easy in-plane magnetocrystalline anisotropy, and a high magnetic transition temperature up to 374 K. The ferromagnetism is found to arise from the hybridization of Ce-$4f/5d$ and I-$5p$ orbitals. When monolayer $\mathrm{Ce}{\mathrm{I}}_{\text{2}}$ is magnetized toward the off-plane $z$ direction, a spontaneous valley polarization as large as 208 meV in the top valence band can be achieved due to the simultaneous breaking of both inversion symmetry and time-reversal symmetry, which is further verified by the perturbation theory of spin-orbital coupling. Also, the anomalous valley Hall effect can be observed…

The effects of the electron-phonon interaction on optical excitations can be understood in terms of exciton-phonon coupling and require a careful treatment in low-dimensional materials with strongly bound excitons or strong electron-hole interaction in general. Through phonon absorption and emission processes, the optically accessible excitons are scattered into otherwise optically dark finite-momentum exciton states. We derive a practical expression for the phonon-induced term of the exciton self-energy (denoted as the exciton-phonon self-energy) that gives the temperature dependence of the optical transition energies and their lifetime broadening resulting from the exciton's interaction with the phonons. We illustrate this theory on a two-dimensional model and show that our expression for the exciton-phonon self-energy differs qualitatively from previous expressions found in the literature that neglect the exciton binding or electron-hole correlations.

In this work, we perform a first-principle study to investigate the atomic and electronic structures of the ${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ van der Waals heterostructure (vdWH) as well as its tunable electronic structure via interlayer coupling and an external perpendicular electric field. The ${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ vdWH is structurally and thermodynamically stable at room temperature. Our results demonstrate that the ${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ vdWH exhibits a semiconducting characteristic with a direct band gap of 1.86/2.66 eV as given by the PBE/HSE06 calculation. This value of band gap conveniently lies in the visible light energy range, thus unraveling the strong optical absorption of ${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ vdWH in the technologically important visible light regime. The band edges of the ${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ vdWH separately from the…

Nonequilibrium dynamics of many-body quantum systems under the effect of measurement protocols is attracting an increasing amount of attention. It has been recently revealed that measurements may induce an abrupt change in the scaling law of the bipartite entanglement entropy, thus suggesting the existence of different nonequilibrium regimes. However, our understanding of how these regimes appear and whether they survive in the thermodynamic limit is much less established. Here we investigate these questions on a one-dimensional quadratic fermionic model: this allows us to reach system sizes relevant in the thermodynamic sense. We show that local projective measurements induce a qualitative modification of the time growth of the entanglement entropy which changes from linear to logarithmic. However, in the stationary regime, the logarithmic behavior of the entanglement entropy does not survive in the thermodynamic limit and, for any finite value of the measurement rate, we numerically show the existence of a single area-law phase for the entanglement entropy. Finally, exploiting the…

Hyperbolic lattices are intricately wired networks that constitute an exciting experimental platform for tabletop simulations of physical models in synthetic negatively curved spaces. This work reveals a hidden crystal order underneath the labyrinthine beauty of such lattices - an order made of unit cells arranged periodically onto the scaffold of a hyperbolic Bravais lattice. This sets the stage for applying powerful techniques from crystallography and band theory to describe experiments in circuit quantum electrodynamics and topoelectrical circuit networks as well as to search for novel phases of matter.

Entanglement dynamics in nonunitary quantum systems have been found to exhibit novel nonequilibrium quantum phase transitions and have attracted tremendous attention with connections to various aspects of quantum information theory. This work establishes, for systems of noninteracting fermions, an exact three-way correspondence between (i) nonunitary (as well as unitary) quantum circuits dynamics in $d$ spatial dimensions; (ii) ($d$+1)-dimensional Gaussian tensor networks, and (iii) fermion systems in ($d$+1) spatial dimensions subject to unitary evolution with static Hamiltonians. Through this correspondence, $d$-dimensional random quantum circuits are connected with the classic subject area of Anderson localization in ($d$+1) spatial dimensions and consequently follow the ``tenfold way'' Altland-Zirnbauer classification. Selected examples of quantum circuits exhibiting entanglement phases and criticalities are used to illustrate these general principles.

The discovery of charge density wave (CDW) order in the kagome-lattice superconductor $A$V${}_{3}$Sb${}_{5}$ is interesting because of the potential interplay between CDW and superconductivity. This paper demonstrates that the CDW order is associated with a sudden hardening of a longitudinal optical phonon mode at the CDW ordering wave vector, thus establishing that the wave vector dependent electron-phonon coupling must play an important role in the CDW order of $A$V${}_{3}$Sb${}_{5}$.

Transport properties are among the most practically important features of materials, yet their precise calculation in strongly interacting systems poses a formidable challenge. One might even expect that it requires a quantum computer. The authors introduce an algorithm that tackles this challenge with only moderate resources on a classical computer. It relies on introducing an artificial dissipation process that only affects nonlocal observables, thus reducing the computational cost without strongly influencing physically relevant quantities. The algorithm is tested on various paradigmatic models with good convergence results.

Non-Hermiticity gives rise to unique topological phases that have no counterparts in Hermitian systems. Such intrinsic non-Hermitian topological phases appear even in one dimension while no topological phases appear in one-dimensional Hermitian systems. Despite the recent considerable interest, the intrinsic non-Hermitian topological phases have been mainly investigated in noninteracting systems described by band theory. It has been unclear whether they survive or reduce in the presence of many-body interactions. Here, we demonstrate that the intrinsic non-Hermitian topological phases in one dimension survive even in the presence of many-body interactions. We formulate a many-body topological invariant by the winding of the complex-valued many-body spectrum in terms of a $\mathrm{U}(1)$ gauge field (magnetic flux). As an illustrative example, we investigate the interacting Hatano-Nelson model and find a unique topological phase and skin effect induced by many-body interactions.

The authors observe here that (a) laser-induced ultrafast demagnetization (UDM) of a metallic ferromagnet $F$ has the same time evolution as (b) terahertz spin transport (TST) from $F$ into an adjacent normal metal $N$. They conclude that UDM in $F$ and TST in $F$|$N$ samples are driven by the same force: (c) a generalized spin voltage, i.e., an excess magnetization of $F$. One can now apply the vast knowledge of UDM to TST to significantly increase spin-current amplitudes for ultrafast spintronic applications.

The non-Hermitian skin effect (NHSE) in non-Hermitian lattice systems, associated with a point gap on the complex energy plane, has attracted great theoretical and experimental interest. Much less is studied on the so-called second-order non-Hermitian skin effect, where the bulk does not support a point gap but localization at the corner still occurs. This work discovers a class of hybrid skin-topological modes as the second-order non-Hermitian skin effect without asymmetric couplings. Specifically, by only adding gain/loss to two-dimensional Chern insulators and so long as the gain/loss strength does not close the line gap, all the topological edge states are localized at one corner under the open boundary condition, with the bulk states extended. The resultant non-Hermitian Chern bands can be still topologically characterized by Chern numbers, whereas the hybrid skin-topological modes are understood via some auxiliary Hermitian systems that belong to either intrinsic or extrinsic second-order topological insulator phases. By proposing an innovative construction of auxiliary…

Hydrides under ultrahigh pressure, such as ${\mathrm{H}}_{3}\mathrm{S}$ and ${\mathrm{LaH}}_{10}$, can achieve coveted superconducting critical temperatures via the conventional electron-phonon coupling mechanism. In this work, we report first-principles investigation of high-temperature phonon-mediated superconductivity in a two-dimensional metal hydride, namely, the Janus MoSH monolayer. The MoSH sheet is a recently synthesized intermediate in realizing Janus transition metal dichalcogenides by involving stripping the top-layer S of ${\mathrm{MoS}}_{2}$ with H atoms [X. Wan et al., ACS Nano 15, 20319 (2021); A. Y. Lu et al., Nat. Nanotechnol. 12, 744 (2017)]. We find coupling of electrons from $\mathrm{Mo}\text{\ensuremath{-}}d$ orbitals around the Fermi level to ultrahigh frequency H- and S-derived phonons, analogous to superconducting hydrides of ${\mathrm{H}}_{3}\mathrm{S}$ and ${\mathrm{LaH}}_{10}$. This leads to strong coupling two-gap superconductivity with the calculated critical temperature ${T}_{c}$ being about 28.58 K at atmosphere pressure. The presence of soft phonon…

We study the Hatano-Nelson model, i.e., a one-dimensional non-Hermitian chain of spinless fermions with nearest-neighbor nonreciprocal hopping, in the presence of repulsive nearest-neighbor interactions. At half filling, we find two $\mathcal{PT}$ transitions, as the interaction strength increases. The first transition is marked by an exceptional point between the first and the second excited state in a finite-size system and is a first-order symmetry-breaking transition into a charge-density wave regime. Persistent currents characteristic of the Hatano-Nelson model abruptly vanish at the transition. The second transition happens at a critical interaction strength that scales with the system size and can thus only be observed in finite-size systems. It is characterized by a collapse of all energy eigenvalues onto the real axis. We further show that in a strong interaction regime, but away from half filling, the many-body spectrum shows point gaps with nontrivial winding numbers, akin to the topological properties of the single-particle spectrum of the Hatano-Nelson chain, which…

We study field theories with global dipole symmetries and gauge dipole symmetries. The famous Lifshitz theory is an example of a theory with a global dipole symmetry. We study in detail its $1+1\mathrm{D}$ version with a compact field. When this global symmetry is promoted to a $U(1)$ dipole gauge symmetry, the corresponding gauge field is a tensor gauge field. This theory is known to lead to fractons. To resolve various subtleties in the precise meaning of these global or gauge symmetries, we place these $1+1\mathrm{D}$ theories on a lattice and then take the continuum limit. Interestingly, the continuum limit is not unique. Different limits lead to different continuum theories, whose operators, defects, global symmetries, etc., are different. We also consider a lattice gauge theory with a ${\mathbb{Z}}_{N}$ dipole gauge group. Surprisingly, several physical observables, such as the ground state degeneracy and the mobility of defects, depend sensitively on the number of sites in the lattice. Our analysis forces us to think carefully about global symmetries that do not act on the…

We investigated the effects of cubic and quartic anharmonicity on lattice dynamics and thermal transport in highly anharmonic ${\mathrm{BaZrO}}_{3}$ crystal over a wide temperature range (300--2000 K) by combining the first-principles-based self-consistent phonon theory and a unified theory of thermal transport including population and coherence contributions. By considering the effects from bubble and loop diagrams, the contributions of both three-phonon (3ph) and four-phonon (4ph) interaction processes to phonon scattering rates and energy shifts were clarified. Anharmonic phonon renormalization is found to play a crucial role in determining the finite-temperature phonon energies and lattice thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{L}}$ in ${\mathrm{BaZrO}}_{3}$. Specifically, the lattice anharmonicity induces significant low-frequency optical phonon hardening at elevated temperatures, which is correlated with the U-shaped potential energy surfaces for these modes. The low-frequency optical phonon hardening significantly suppresses phonon scattering rates by altering…

Ferrovalley and topology are two basic concepts in both fundamental research fields and emerging device applications. So far, reports are extremely scarce regarding the coupling of these two scenarios in a single material system. By first-principles calculations and Monte Carlo simulations, we predict a highly stable intrinsic ferrovalley $2H\text{\ensuremath{-}}{\mathrm{RuCl}}_{\text{2}}$ semiconductor with an easy out-of-plane magnetization and a high Curie temperature of 260 K. Due to the combination of exchange interaction and spin-orbit coupling, the system exhibits a spontaneous valley polarization of 240 meV in the top valence band, which is further confirmed by a first-order perturbation theory. Moreover, its out-of-plane ferromagnetic ordering can remain rather robust and survive up to 547 K under $\ensuremath{-}5$% compressive strain well above room temperature. On the other hand, the application of tensile strain can drive the system from the ferrovalley phase into a half-valley-metal state with 100% spin and valley polarizations, followed then by a quantum anomalous Hall…

Due to its transparent and highly dispersive nature, plasmonically induced transparency (PIT) has become an attractive field in the on-chip control of light. Conventional methods to achieve PIT are only limited to the lowest dipole-dipole or dipole-combined quadrupole modes by breaking structural symmetry. Consequently, a general methodological framework for accurately designing all-order PIT remains absent. In this paper, we propose a theoretical scheme to achieve unidirectional odd-to-even order PIT by establishing a model with two layers of periodic graphene nanoribbons. The underlying physical principles are uncovered by defining the additional resonant phase of one mode over the other as phase difference, which predicts that the PIT effects appear (disappear) generally near the positions where the phase difference is around odd (even) multiple numbers of \ensuremath{\pi}. Full-wave simulations and theoretical analysis are used to demonstrate our proposal, revealing that the proposed PIT concept possesses good robustness against both the ribbon width and the relative ribbon…

We establish a direct connection between general tensor networks and deep feed-forward artificial neural networks. The core of our results is the construction of neural-network layers that efficiently perform tensor contractions and that use commonly adopted nonlinear activation functions. The resulting deep networks feature a number of edges that closely match the contraction complexity of the tensor networks to be approximated. In the context of many-body quantum states, this result establishes that neural-network states have strictly the same or higher expressive power than practically usable variational tensor networks. As an example, we show that all matrix product states can be efficiently written as neural-network states with a number of edges polynomial in the bond dimension and depth that is logarithmic in the system size. The opposite instead does not hold true, and our results imply that there exist quantum states that are not efficiently expressible in terms of matrix product states or projected entangled pair states but that are instead efficiently expressible with…

The critical current of a superconductor can depend on the direction of current flow due to magnetochiral anisotropy when both inversion and time-reversal symmetry are broken, an effect known as the superconducting (SC) diode effect. Here, we consider one-dimensional (1D) systems in which superconductivity is induced via the proximity effect. In both topological insulator and Rashba nanowires, the SC diode effect due to a magnetic field applied along the spin-polarization axis and perpendicular to the nanowire provides a measure of inversion symmetry breaking in the presence of a superconductor. Furthermore, a strong dependence of the SC diode effect on an additional component of magnetic field applied parallel to the nanowire as well as on the position of the chemical potential can be used to detect that a device is in the region of parameter space where the phase transition to topological superconductivity is expected to arise.

Experiments in the recently discovered vanadium-based kagome metals have suggested that their charge-ordered state displays not only bond distortions, characteristic of a ``real'' charge density wave (rCDW), but also time-reversal symmetry breaking, typical of loop currents described by an ``imaginary'' charge density wave (iCDW). Here, we combine density-functional theory, group theory, and phenomenological modeling to investigate the complex charge-ordered states that arise from interactions between the low-energy van Hove singularities present in the electronic structure of $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$. We find two broad classes of mixed iCDW-rCDW configurations: triple-$\mathbf{Q}$ iCDW, triple-$\mathbf{Q}$ rCDW order, dubbed $3\mathbf{Q}\text{\ensuremath{-}}3\mathbf{Q}$, and double-$\mathbf{Q}$ iCDW, single-$\mathbf{Q}$ rCDW order, dubbed $2\mathbf{Q}\text{\ensuremath{-}}1\mathbf{Q}$. Moreover, we identify seven different types of iCDW order, stemming from the different vanadium-orbital and kagome-sublattice structures of the two pairs of van Hove singularities present…

We report x-ray diffraction studies of the electronic ordering instabilities in the kagome material ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ as a function of temperature and applied magnetic field. Our zero-field measurements between 10 and 120 K reveal an unexpected reorganization of the three-dimensional electronic order in the bulk of ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$: At low temperatures, a $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ superstructure modulation due to electronic order is observed, which upon warming changes to a $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}4$ superstructure at 60 K. The electronic order-order transition discovered here involves a change in the stacking of electronically ordered ${\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ layers, which coincides with anomalies previously observed in magnetotransport measurements. This implies that the temperature-dependent three-dimensional electronic order plays a decisive role for transport properties, which are related to the Berry curvature of the V bands. We…

The interplay between unitary dynamics and local quantum measurements results in unconventional nonunitary dynamical phases and transitions. In this paper we investigate the dynamics of $(d+1)$-dimensional hybrid stabilizer circuits, for $d=1,2,3$. We characterize the measurement-induced phases and their transitions using large-scale numerical simulations focusing on entanglement measures, purification dynamics, and wave-function structure. Our findings demonstrate the measurement-induced transition in $(d+1)$ spatiotemporal dimensions is conformal and has critical properties close to the percolation transition in $(d+1)$ spatial dimensions.

Understanding the nature of the exotic CDW order is of crucial importance for uncovering its origin in the kagome superconductors $A$V${}_{3}$Sb${}_{5}$. Here, using angle-resolved photoemission spectroscopy, the authors reveal characteristic double-band splittings and band reconstructions as well as band-folding gaps in the CDW phase. By combining the findings with density functional theory calculations, they demonstrate that two representative distortions in the kagome lattice - the star of David and the trihexagonal ones - intrinsically coexist in the CDW of CsV${}_{3}$Sb${}_{5}$.

We theoretically investigate asymmetric two-junction SQUIDs with different current-phase relations in the two Josephson junctions, involving higher Josephson harmonics. Our main focus is on the ``minimal model'' with one junction in the SQUID loop possessing the sinusoidal current-phase relation and the other one featuring additional second harmonic. The current-voltage characteristic (CVC) turns out to be asymmetric, $I(\ensuremath{-}V)\ensuremath{\ne}\ensuremath{-}I(V)$. The asymmetry is due to the presence of the second harmonic and depends on the magnetic flux through the interferometer loop, vanishing only at special values of the flux such as integer or half-integer in the units of the flux quantum. The system thus demonstrates the flux-tunable Josephson diode effect (JDE), the simplest manifestations of which is the direction dependence of the critical current. We analyze asymmetry of the overall $I(V)$ shape both in the absence and in the presence of external ac irradiation. In the voltage-source case of external signal, the CVC demonstrates the Shapiro spikes. The integer…

Strain is an effective method to tune the electronic properties of two-dimensional (2D) materials and can induce novel phase transition. Recently, the 2D $M{A}_{2}{Z}_{4}$ family of materials has attracted interest because of their emerging topological, magnetic, and superconducting properties. Here, we investigate the impact of strain effects ($a/{a}_{0}$ = 0.96--1.04) on the physical properties of the Janus monolayer ${\mathrm{VSiGeN}}_{4}$ as a derivative of ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ or ${\mathrm{VGe}}_{2}{\mathrm{N}}_{4}$, which possesses dynamical, mechanical, and thermal stabilities. For out-of-plane magnetic anisotropy, with increasing strain, ${\mathrm{VSiGeN}}_{4}$ undergoes a transition between a ferrovalley semiconductor (FVS), half-valley metal (HVM), valley-polarized quantum anomalous Hall insulator, HVM, and FVS. These effects imply twice topological phase transitions, which are related to the sign-reversible Berry curvature and band inversion between ${d}_{xy}+{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals for the $K$ or $\ensuremath{-}K$…

Recent progress in understanding thermal transport in complex crystals has highlighted the prominent role of heat conduction mediated by interband tunneling processes, which emerge between overlapping phonon bands (i.e., with energy differences smaller than their broadenings). These processes have recently been described in different ways, relying on the Wigner or Green-Kubo formalism, leading to apparently different results, which question the definition of the heat-current operator. Here, we implement a full quantum approach based on the Kubo formula, elucidating analogies and differences with the recently introduced Wigner or Green-Kubo formulations, and extending the description of thermal transport to the overdamped regime of atomic vibrations, where the phonon quasiparticle picture breaks down. We rely on first-principles calculations on complex crystals with ultralow conductivity to compare numerically the thermal conductivity obtained within the aforementioned approaches, showing that at least in the quasiparticle regime the differences are negligible for practical…

Nonreciprocal responses of noncentrosymmetric quantum materials attracted recent intensive interests, which is essential for the rectification function in diodes. A recent breakthrough is the discovery of superconducting diode effect. The principle to enlarge the rectification effect is highly desired to guide the design of the superconducting diode. Here, we study theoretically the Josephson junction S/FI/S (S: $d$-wave superconductor, FI: ferromagnetic insulator) on the surface of a topological insulator (TI). The simultaneous existence of $sin\ensuremath{\varphi}$, $cos\ensuremath{\varphi}$, and $sin2\ensuremath{\varphi}$ terms with almost the same order in the Josephson current $I(\ensuremath{\varphi})$ is essential to get larger values of the $Q$ factor given by $Q=({I}_{c}^{+}\ensuremath{-}|{I}_{c}^{\ensuremath{-}}|)/({I}_{c}^{+}+|{I}_{c}^{\ensuremath{-}}|)$ with ${I}_{c}^{+}=\mathrm{max}[I(\ensuremath{\varphi})]$ and the negative one ${I}_{c}^{\ensuremath{-}}$ for the macroscopic phase difference $\ensuremath{\varphi}$ of two superconductors on TI. We find that it can show a…

The orbital Hall effect (OHE) designates the generation of a charge-neutral flow of orbital angular momentum transverse to an initial charge current. Recent theoretical investigations suggest that transition metals display sizable OHE, encouraging experimental search along this direction. Nonetheless, most of these theories assume that the orbital moment originates from the region centered on the atomic sites, adopting the so-called atom-centered approximation. In periodic crystals though, the motion of the wave packet between atoms provides a crucial contribution to the overall orbital moment, and neglecting it can lead to a severe misestimation of the OHE. By applying the ``modern theory'' of orbital magnetization to the OHE, we assess the relative importance of intra- and interatomic contributions in selected materials from first principles. We find that whereas the OHE is mostly of intra-atomic origin for wide band-gap semiconductors (e.g., ${\mathrm{MoS}}_{2}$), the interatomic contribution becomes crucial in narrow band-gap semiconductors (SnTe, PbTe) and transition metals…

The kagome metals $A$V${}_{3}$Sb${}_{5}$ ($A$ = Cs, Rb, and K) host a wide range of exotic physics, including charge density wave, superconductivity, and topological state. Here, the authors present high-pressure resistance measurements on RbV${}_{3}$Sb${}_{5}$ and KV${}_{3}$Sb${}_{5}$. Two superconducting domes under pressure are unambiguously observed in both compounds, as they were previously observed in CsV${}_{3}$Sb${}_{5}$. The authors construct an integrated temperature-pressure phase diagram of $A$V${}_{3}$Sb${}_{5}$, showing that double-dome superconductivity under pressure is a common feature of these V-based kagome metals.

One big achievement in modern condensed matter physics is the recognition of the importance of various band geometric quantities in physical effects. As prominent examples, Berry curvature and the Berry curvature dipole are connected to the linear and the second-order Hall effects, respectively. Here, we show that the Berry connection polarizability (BCP) tensor, as another intrinsic band geometric quantity, plays a key role in the third-order Hall effect. Based on the extended semiclassical formalism, we develop a theory for the third-order charge transport and derive explicit formulas for the third-order conductivity. Our theory is applied to the two-dimensional (2D) Dirac model to investigate the essential features of the BCP and the third-order Hall response. We further demonstrate the combination of our theory with the first-principles calculations to study a concrete material system, the monolayer FeSe. Our work establishes a foundation for the study of third-order transport effects, and reveals the third-order Hall effect as a tool for characterizing a large class of…

The two-dimensional quantum spin model proposed by Shastry and Sutherland more than four decades ago is notable for its realization in SrCu${}_{2}$(BO${}_{3}$)${}_{2}$. Here, the authors present numerical evidence of a gapless spin liquid phase in the model and discuss its connection to a deconfined quantum critical point. The new phase exists in a parameter regime where recent high-pressure heat capacity measurements on SrCu${}_{2}$(BO${}_{3}$)${}_{2}$ did not detect any low-temperature order, in contrast to the antiferromagnetic and plaquette-singlet phases existing at higher and lower pressures, respectively. Thus, the elusive spin liquid may exist in SrCu${}_{2}$(BO${}_{3}$)${}_{2}$.

In this work, we find that the complexity of quantum many-body states, defined as a spread in the Krylov basis, may serve as a probe that distinguishes topological phases of matter. We illustrate this analytically in one of the representative examples, the Su-Schrieffer-Heeger model, finding that spread complexity becomes constant in the topological phase. Moreover, in the same setup, we analyze exactly solvable quench protocols where the evolution of the spread complexity shows distinct dynamical features depending on the topological vs nontopological phase of the initial state as well as the quench Hamiltonian.

While the band theory of non-Hermitian Hamiltonians and the dynamics they generate have received considerable recent interest, the quantum steady states of such models remain largely unexplored. Here, the authors systematically characterize such states for fermions and bosons using an open quantum system approach. Surprisingly, these steady states exhibit features that cannot be extracted readily from the non-Hermitian Hamiltonian. This includes a macroscopic length scale which characterizes the steady-state occupation but differs from the localization length of the eigenvectors.

Two-dimensional Janus structures with vertical intrinsic electric fields exhibit many interesting physical properties that are not possible with symmetric materials. We systematically investigate the structural, electronic, and transport properties of quintuple-layer atomic Janus ${\mathrm{Ga}}_{2}\mathrm{S}{X}_{2}$ ($X=$ O, S, Se, Te) monolayers using the first-principles calculations. The stability of the Janus structures is evaluated via the analysis of their phonon dispersion curves, cohesive and formation energies, and elastic constants. The existence of a vertical internal electric field due to the lack of mirror symmetry has resulted in a vacuum level difference between the two sides of the investigated Janus structures. At the ground state, while the Janus ${\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{O}}_{2}$ is metallic, the other three configurations (${\mathrm{Ga}}_{2}{\mathrm{S}}_{3}, {\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{Se}}_{2}$, and ${\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{Te}}_{2}$) are semiconductors with indirect band gaps. The electronic properties of…

Strong long-range coupling between distant spins is crucial for spin-based quantum information processing. However, achieving such a strong spin-spin coupling remains challenging. Here we propose to realize a strong coupling between two distant spins via the Kerr effect of magnons in a yttrium-iron-garnet nanosphere. By applying a microwave field on this nanosphere, the Kerr effect of magnons can induce the magnon squeezing, so that the coupling between the spin and the squeezed magnons can be exponentially enhanced. This in turn allows the spin-magnon distance to increase from nano- to micrometer scale. By considering the virtual excitation of the squeezed magnons in the dispersive regime, strong spin-spin coupling mediated by the squeezed magnons can be achieved, and a remote quantum-state transfer, as well as the nonlocal two-qubit iswap gate with high fidelity becomes implementable. Our approach offers a feasible scheme to perform quantum information processing among distant spins.

Scar states are special many-body eigenstates that weakly violate the eigenstate thermalization hypothesis (ETH). Using the explicit formalism of the Lanczos algorithm, usually known as the forward scattering approximation in this context, we compute the Krylov state (spread) complexity of typical states generated by the time evolution of the PXP Hamiltonian, hosting such states. We show that the complexity for the N\'eel state revives in an approximate sense, while complexity for the generic ETH-obeying state always increases. This can be attributed to the approximate SU(2) structure of the corresponding generators of the Hamiltonian. We quantify such ``closeness'' by the $q$-deformed SU(2) algebra and provide an analytic expression of Lanczos coefficients for the N\'eel state within the approximate Krylov subspace. We intuitively explain the results in terms of a tight-binding model. We further consider a deformation of the PXP Hamiltonian and compute the corresponding Lanczos coefficients and the complexity. We find that complexity for the N\'eel state shows nearly perfect…

Multiferroic van der Waals (vdW) heterostrucutres offer an exciting route toward high-performance nanoelectronics and spintronics device technology. Here we investigate the electronic and transport properties of multiferroic vdW heterostructures composed of a ferromagnetic ${\mathrm{FeCl}}_{2}$ monolayer and a ferroelectric ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$ monolayer using first-principles density functional theory and quantum transport simulations. We show that ${\mathrm{FeCl}}_{2}/{\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$ heterostructure can be reversibly switched from semiconducting to half-metallic behavior by electrically modulating the ferroelectric polarization states of ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$. Intriguingly, the half-metallic phase exhibits a type-III broken gap-band alignment, which can be beneficial for tunneling field-effect transistor applications. We perform a quantum transport simulation based on a proof-of-concept two-terminal nanodevice to demonstrate all-electric-controlled valving effects uniquely enabled by the nonvolatile ferroelectric switching of the…

We propose and theoretically investigate an alternative way to create the poor man's Majorana bound states (MBSs) introduced in Phys. Rev. B 86, 134528 (2012). Our proposal is based on two quantum dots (QDs) with strong electron-electron interactions that couple via a central QD with proximity-induced superconductivity. In the presence of spin-orbit coupling and a magnetic field, gate control of all three QDs allows tuning the system into sweet spots with one MBS localized on each outer dot. We quantify the quality of these MBSs and show how it depends on the Zeeman energy and interaction strength. We also show how nonlocal transport spectroscopy can be used to identify sweet spots with high MBS quality. Our results provide a path for investigating MBS physics in a setting that is free of many of the doubts and uncertainties that plague other platforms.

Mismatched lattice constants at a van der Waals epitaxy interface often introduce in-plane strains to the lattice of the epitaxial layer, termed epitaxy strain, wherein the strains do not follow the intralayer Poisson's relation. In this study, we obtained the magnetic phase diagrams of ${\mathrm{CrSe}}_{2}$ and ${\mathrm{CrTe}}_{2}$ mono- and bilayers under epitaxy strain up to 8%, as predicted using density functional theory calculations. The magnetic phase diagrams indicate that the in-plane epitaxy strain manipulates either the intra- or interlayer magnetism. The in-plane strain varies the interlayer distance, defined using an interlayer Poisson's ratio, which determines whether the interlayer magnetism follows a Bethe--Slater curve-like (BSC-like) or a reversed BSC-like behavior, depending on the in-plane magnetism. The tunability of the intralayer magnetism is a result of competing intralayer Cr--Cr superexchange interactions. A graphene substrate was introduced to examine the validity of our diagrams in practice. This study also afforded a tentative explanation on the…

Non-Hermitian systems exhibit nontrivial band topology and a strong sensitivity of the energy spectrum on the boundary conditions. Remarkably, a macroscopic number of bulk states get squeezed toward the lattice edges under open boundary conditions, an effect dubbed the non-Hermitian skin effect (NHSE). A well-established dynamical signature of the NHSE in real space is the directional bulk flow (or persistent current) for arbitrary initial excitation of the system, which is observed at long times. Here we unravel a different dynamical signature of the NHSE in real space that manifests itself in the early-time dynamics of the system, namely, self-acceleration of the wave function. Self-acceleration is demonstrated to occur rather generally in single--band lattice models probed by single-site excitation, where the acceleration turns out to be proportional to the area enclosed by the energy spectrum of the Bloch Hamiltonian under periodic boundary conditions. The observation of wave packet self-acceleration at early times is a clear signature of the NHSE and should be experimentally…

We study a simple model of interacting bosons on a $d$-dimensional cubic lattice whose dynamics conserves both total boson number and total boson dipole moment. This model provides a simple framework in which several remarkable consequences of dipole conservation can be explored. As a function of chemical potential and hopping strength, the model can be tuned between gapped Mott insulating phases and various types of gapless condensates. The condensed phase realized at large hopping strengths, which we dub a Bose-Einstein insulator, is particularly interesting: despite having a Bose condensate, it is insulating, and despite being an insulator, it is compressible.

Band topology is both constrained and enriched by the presence of symmetry. The importance of antiunitary symmetries such as time reversal was recognized early on leading to the classification of topological band structures based on the ten-fold way. Since then, lattice point group and nonsymmorphic symmetries have been seen to lead to a vast range of possible topologically nontrivial band structures many of which are realized in materials. In this paper, we show that band topology is further enriched in many physically realizable instances where magnetic and lattice degrees of freedom are wholly or partially decoupled. The appropriate symmetry groups to describe general magnetic systems are the spin-space groups. Here we describe cases where spin-space groups are essential to understand the band topology in magnetic materials. We then focus on magnon band topology where the theory of spin-space groups has its simplest realization. We consider magnetic Hamiltonians with various types of coupling including Heisenberg and Kitaev couplings revealing a hierarchy of enhanced magnetic…

Magnon-phonon scattering (MPS) has attracted widespread attention in quantum heat/spin transport across the ferromagnetic/nonmagnetic (F/N) interfaces, with the rapid progress of experiments on spin caloritronics in recent years. However, the lack of theoretical methods, accounting for the MPS rigorously, has seriously hindered investigations on the quantum heat transport in magnetic nanostructures with broken translational symmetry, such as F/N interfaces. In this paper, we propose a theoretical formalism of the nonequilibrium Green function to incorporate the MPS into the quantum heat transport for three-dimensional ferromagnetic nanostructures, rigorously, through a diagrammatic perturbation analysis. A computational scheme is developed for the first-principles simulation of quantum heat transport in practical magnetic nanostructures, and a generalized formalism of heat flow is presented for the analysis of the elastic and inelastic process of heat transport. A thermal rectification driven by MPS is observed in the numerical simulation of heat transport across the F/N interface…

First-principles structure prediction enables the computational discovery of materials with extreme, or exotic properties. A notable example being the dense hydrides, which, following computational searches, were found to exhibit high-${T}_{c}$ superconductivity. The rapid construction of ephemeral, or disposable, interatomic potentials, dramatically accelerates the exploration of energy landscapes, even accounting for the time to create the potentials. This approach is used to uncover a complex and overlooked phase of dense silane, suggesting that the binary hydrides should be revisited.

Electronic materials harbor a plethora of exotic quantum phases, ranging from unconventional superconductors to non-Fermi liquids and, more recently, topological phases of matter. While these quantum phases in integer dimensions are well characterized by now, their presence in fractional dimensions remains vastly unexplored. Here, we theoretically show that a special class of crystalline phases, namely, higher-order topological phases that via an extended bulk-boundary correspondence feature robust gapless modes on lower-dimensional boundaries, such as corners and hinges, can be found on a representative family of fractional materials: quantum fractals. To anchor this general proposal, we demonstrate realizations of second-order topological insulators and superconductors, supporting charged and neutral Majorana corner modes on planar Sierpi\ifmmode \acute{n}\else \'{n}\fi{}ski carpet and triangle fractals, respectively. These predictions can be experimentally tested on designer electronic fractal materials, as well as on various highly tunable metamaterial platforms, such as…

We demonstrate the universal properties of dissipative Tomonaga-Luttinger (TL) liquids by calculating correlation functions and performing finite-size scaling analysis of a non-Hermitian XXZ spin chain as a prototypical model in one-dimensional open quantum many-body systems. Our analytic calculation is based on effective field theory with bosonization, finite-size scaling approach in conformal field theory, and the Bethe-ansatz solution. Our numerical analysis is based on the density-matrix renormalization group generalized to non-Hermitian systems (NH-DMRG). We uncover that the model in the massless regime with weak dissipation belongs to the universality class characterized by the complex-valued TL parameter, which is related to the complex generalization of the $c=1$ conformal field theory. As the dissipation strength increases, the values of the TL parameter obtained by the NH-DMRG begin to deviate from those obtained by the Bethe-ansatz analysis, indicating that the model becomes massive for strong dissipation. Our results can be tested with the two-component Bose-Hubbard…

We report a high-throughput ab initio study of the thermodynamic and superconducting properties of the recently synthesized $X{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ clathrates. These compounds, in which boron and carbon form a spongelike network of interconnected cages each enclosing a central $X$ atom, are attractive candidates to achieve high-${T}_{c}$ conventional superconductivity at ambient pressure, due to the simultaneous presence of a stiff B-C covalent network and a tunable Fermi energy due to the $X$ atom acting as a charge reservoir. Ternary compounds like ${\mathrm{CaB}}_{3}{\mathrm{C}}_{3}, {\mathrm{SrB}}_{3}{\mathrm{C}}_{3}$, and ${\mathrm{BaB}}_{3}{\mathrm{C}}_{3}$ are predicted to exhibit ${T}_{c} \ensuremath{\lesssim}50$ K at moderate or ambient pressures, which may further increase up to 77 K if the original compounds are hole doped, by replacing the divalent alkaline earth with a monovalent alkali metal to form an ordered $XY{\mathrm{B}}_{6}{\mathrm{C}}_{6}$ alloy.

The recent experimental discovery of spin-valley symmetry breaking phases and superconductivity in rhombohedral trilayer graphene has generated much excitement. This research attempts to provide theoretical understanding of these phases. A prominent feature of the system is the existence of van Hove singularities in the electronic band structure. Under interactions, these electronic states exhibit a high tendency toward intervalley coherence (IVC) ordering. Upon doping, the IVC order can melt, and the low-lying IVC fluctuations can mediate superconductivity with spin-singlet pairing.

Strontium titanate ($\mathrm{SrTi}{\mathrm{O}}_{3}$) is regarded as an essential material for oxide electronics. One of its many remarkable features is the subtle structural phase transition, driven by the antiferrodistortive lattice mode, from a high-temperature cubic phase to a low-temperature tetragonal phase. Classical molecular dynamics (MD) simulation is an efficient technique to reveal atomistic features of phase transition, but its application is often limited by the accuracy of empirical interatomic potentials. Here, we develop an accurate deep potential (DP) model of $\mathrm{SrTi}{\mathrm{O}}_{3}$ based on a machine learning method using data from first-principles density functional theory (DFT) calculations. The DP model has DFT-level accuracy, capable of performing efficient MD simulations and accurate property predictions. Using the DP model, we investigate the temperature-driven cubic-to-tetragonal phase transition and construct the in-plane biaxial strain-temperature phase diagram of $\mathrm{SrTi}{\mathrm{O}}_{3}$. The simulations demonstrate that the strain-induced…

Based on first-principles calculations and symmetry analysis, we predict atomically thin ($1\ensuremath{-}N$ layers) $2H$ group-VIB transition metal dichalcogenides (TMDs) $M{X}_{2}$ ($M$ = Mo, W; $X$ = S, Se, Te) are large-gap higher-order topological crystalline insulators (HOTCIs) protected by ${C}_{3}$ rotation symmetry. We explicitly demonstrate the nontrivial topological indices and the existence of hallmark corner states with quantized fractional charge for these familiar TMDs with a large bulk optical band gap ($1.64\text{--}1.95\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ for the monolayers), which would facilitate the experimental verification and exploration of the HOTCI states. Furthermore, we find that the well-defined corner states exist in the triangular finite-size flakes with armchair edges of the atomically thin ($1\ensuremath{-}N$ layers) $2H$ group-VIB TMDs, and the corresponding quantized fractional charge is the number of layers $N$ modulo three. The fractional corner charge will double when spin degree of freedom is taken into account.

Recent studies have shown that moir\'e flat bands in twisted bilayer graphene (TBG) can acquire nontrivial Berry curvatures when aligned with a hexagonal boron nitride substrate, which can be manifested as a correlated Chern insulator near the 3/4 filling. In this Letter, we show that the large Berry curvatures in the moir\'e bands lead to a strong nonlinear Hall (NLH) effect in strained TBG with general filling factors. Under a weak uniaxial strain $\ensuremath{\sim}0.1%$, the Berry curvature dipole which characterizes the nonlinear Hall response can be as large as $\ensuremath{\sim}200\phantom{\rule{0.28em}{0ex}}\text{\AA{}}$, exceeding the values of previously known nonlinear Hall materials by two orders of magnitude. The dependence of the giant NLH effect as a function of electric gating, strain, and twist angle is further investigated systematically. Importantly, we point out that the giant NLH effect appears generically for a twist angle near the magic angle due to the strong susceptibility of nearly flat moir\'e bands to symmetry breaking induced by strains, which can even…

Global optimization with first-principles energy expressions (GOFEE) is an efficient method for identifying low-energy structures in computationally expensive energy landscapes such as the ones described by density functional theory (DFT), van der Waals enabled DFT, or even methods beyond DFT. GOFEE is an evolutionary algorithm, that in order to explore configuration space creates several candidates in parallel. These are treated approximately using a machine learned surrogate model of energies and forces, trained on the fly, eliminating the need for expensive relaxations using first-principles methods. Eventually, using Bayesian statistics, GOFEE chooses one candidate and treats that at the full first-principles level. In this paper we elaborate on the importance of the use of a Gaussian kernel with two length scales in the Gaussian process regression surrogate model. We further explore the role of the use in GOFEE of the lower confidence bound for relaxation and selection of candidate structures. In addition, we present details of a sampling scheme for obtaining parent structures…

We report the observation of twofold rotation symmetry in charge-density wave (CDW) state in the newly discovered kagome superconductor ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$. Just below its CDW transition temperature (${T}_{\mathrm{CDW}}$), the polarization rotation of the reflected laser beam promptly emerges and increases close to about 1 mrad, and the rotation angle shows twofold rotation symmetry. This observation is very different from many other experimental methods in which nematicity or ${\mathrm{C}}_{2}$ rotation symmetry appears at low temperatures far below ${T}_{\mathrm{CDW}}$. There are two components included, where the $d$-wave-like component originates from electronic nematic order and constant term points to the possible existence of time-reversal-symmetry breaking (TRSB), respectively. With femtosecond laser pulse pumping, the likely TRSB and nematicity can be easily suppressed, and the latter is further modulated by coherent phonon. Our investigation provides clear optical evidence for the formation of nematic order with twofold rotation symmetry and possible…

We investigate entanglement dynamics in continuously monitored open quantum systems featuring current-carrying nonequilibrium states. We focus on a prototypical one-dimensional model of boundary-driven noninteracting fermions with monitoring of the local density, whose average Lindblad dynamics features a well-studied ballistic to diffusive crossover in transport. Here we analyze the dynamics of the fermionic negativity, mutual information, and purity along different quantum trajectories. We show that monitoring this boundary-driven system enhances its entanglement negativity at long times, which otherwise decays to zero in the absence of measurements. This result is in contrast with the case of unitary evolution where monitoring suppresses entanglement production. For small values of $\ensuremath{\gamma}$, the stationary-state negativity shows a logarithmic scaling with system size, transitioning to an area-law scaling as $\ensuremath{\gamma}$ is increased beyond a critical value. Similar critical behavior is found in the mutual information, while the late-time purity shows no…

Tremendous interest has recently emerged in the kagome metal superconductors, since they are associated with an unconventional multicomponent charge density wave order parameter that may break time-reversal symmetry or obey other uncommon properties required for unconventional superconductivity. Here, the authors present spectroscopic evidence for the interplay between interacting order parameter components. The authors further develop a free-energy model and consistently describe experimental data, providing a basis for studying the interplay between multicomponent orders in the kagome metal systems.

We present a multiscale density functional theory (DFT) informed molecular dynamics and tight-binding approach to capture the interdependent atomic and electronic structures of twisted bilayer graphene. We calibrate the flat band magic angle to be at ${\ensuremath{\theta}}_{\mathrm{M}}=1.{08}^{\ensuremath{\circ}}$ by rescaling the interlayer tunneling for different atomic structure relaxation models as a way to resolve the indeterminacy of existing atomic and electronic structure models whose predicted magic angles vary widely between $0.{9}^{\ensuremath{\circ}}$ and $1.{3}^{\ensuremath{\circ}}$. The interatomic force fields are built using input from various stacking and interlayer distance-dependent DFT total energies including the exact exchange and random phase approximation ($\mathrm{EXX}+\mathrm{RPA}$). We use a Fermi velocity of ${\ensuremath{\upsilon}}_{\mathrm{F}}\ensuremath{\simeq}{10}^{6}$ m/s for graphene that is enhanced by $\ensuremath{\sim}15%$ over the local density approximation (LDA) values. Based on this atomic and electronic structure model we obtain…

The explorations of non-Hermiticity have been devoted to investigate the disorder-induced many-body localization (MBL). However, the sensitivity of the spatial boundary conditions and the interplay of the non-Hermitian skin effect with many-body phenomena are not yet clear. For a MBL system in the presence of nonreciprocal tunnelings and random disorder potential, we identify two different complex-real spectral transitions, one is present for both open and periodic boundaries while the other is present only for open boundaries of coupled non-Hermitian chains. The later is driven due to the interchain coupling at weak disorder where the level statistics of the real eigenenergy phase follows a Gaussian orthogonal ensemble. We further characterize wave functions through the (biorthogonal) inverse participation ratio and fractal dimension, which reveal the suppression of skin effect in the non-Hermitian MBL phase. Finally, we demonstrate that the quench dynamics of the local particle density, spin imbalance, and entanglement entropy also signify the hallmark of the boundary effects and…

Erbium-doped materials can serve as spin-photon interfaces with optical transitions in the telecom $C$ band, making them an exciting class of materials for long-distance quantum communication. However, the spin and optical coherence times of ${\mathrm{Er}}^{3+}$ ions are limited by currently available host materials, motivating the development of new ${\mathrm{Er}}^{3+}$-containing materials. Here we demonstrate the use of ion implantation to efficiently screen prospective host candidates, and show that disorder introduced by ion implantation can be mitigated through post-implantation thermal processing to achieve inhomogeneous linewidths comparable to bulk linewidths in as-grown samples. We present optical spectroscopy data for each host material, which allows us to determine the level structure of each site, allowing us to compare the environments of ${\mathrm{Er}}^{3+}$ introduced via implantation and via doping during growth. We demonstrate that implantation can generate a range of local environments for ${\mathrm{Er}}^{3+}$, including those observed in bulk-doped materials, and…

We study the emergence of superconductivity in rhombohedral trilayer graphene due purely to the long-range Coulomb repulsion. This repulsive-interaction-driven phase in rhombohedral trilayer graphene (RTG) is significantly different from those found in twisted bilayer and trilayer graphenes. In the latter case, the nontrivial momentum-space geometry of the Bloch wave functions contributes to an effective attractive electron--electron interaction; this allows for less modulated order parameters and for spin-singlet pairing. In RTG, we instead find spin-triplet superconductivity with critical temperatures up to $\ensuremath{\sim}0.15$ K. The critical temperatures strongly depend on electron filling and peak where the density of states diverge. The order parameter shows a significant modulation within each valley pocket of the Fermi surface.

Compounds with kagome lattice usually host many exotic quantum states, including the quantum spin liquid, non-trivial topological Dirac bands and a strongly renormalized flat band, etc. Recently an interesting vanadium based kagome family $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ $(A=\mathrm{K},\mathrm{Rb},\text{or}\phantom{\rule{0.28em}{0ex}}\mathrm{Cs})$ was discovered, and these materials exhibit multiple interesting properties, including unconventional saddle-point driving charge density wave (CDW) state, superconductivity, etc. Furthermore, some experiments show the anomalous Hall effect which inspires us to believe that there might be some chiral flux current states. Here we report scanning tunneling measurements by using spin-polarized tips. Although we have observed clearly the $2{a}_{0}\ifmmode\times\else\texttimes\fi{}2{a}_{0}$ CDW and $4{a}_{0}$ stripe orders, the well-designed experiments with refined spin-polarized tips do not reveal any trace of the chiral flux current phase in ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ within the limits of experimental accuracy. No observation…

A Fermi surface coupled to a scalar field can be described in a $1/N$ expansion by choosing the fermion-scalar Yukawa coupling to be random in the $N$-dimensional flavor space, but invariant under translations. We compute the conductivity of such a theory in two spatial dimensions for a critical scalar. We find a Drude contribution, and verify that the proposed $1/{\ensuremath{\omega}}^{2/3}$ contribution to the optical conductivity at frequency $\ensuremath{\omega}$ has vanishing coefficient for a convex Fermi surface. We also describe the influence of impurity scattering of the fermions, and find that while the self-energy resembles a marginal Fermi liquid, the resistivity and optical conductivity behave like a Fermi liquid.

Recently, great effort has been devoted to the search for two-dimensional (2D) ferromagnetic materials with inherent strong Dzyaloshinskii-Moriya interaction (DMI). Here, through a first-principles approach, we systematically investigate the effect of biaxial strain on the DMI, the Heisenberg exchange interaction, and the magnetic anisotropy energy (MAE) of Janus ${\mathrm{Cr}}_{2}{X}_{3}{Y}_{3}$ ($X,Y$ = Cl, Br, I, $X\ensuremath{\ne}Y$) monolayers. Both DMI and MAE can be significantly enhanced by tensile strain, whereas a reversal of the chirality of DMI in ${\mathrm{Cr}}_{2}{\mathrm{Cl}}_{3}{\mathrm{Br}}_{3}$ and a switch of MAE from off plane to in plane in ${\mathrm{Cr}}_{2}{\mathrm{I}}_{3}{\mathrm{Cl}}_{3}$ are induced by a compressive strain of $2%$. Microscopically, DMI and MAE are associated mainly with the large spin-orbit coupling of the heavy nonmagnetic halogen atoms rather than that of the magnetic Cr atoms. In particular, the peculiar magnetic transition of ${\mathrm{Cr}}_{2}{\mathrm{I}}_{3}{\mathrm{Cl}}_{3}$ is explained by competition between direct exchange and…

A remarkable feature of the trimer Su-Schrieffer-Heeger (SSH3) model is that it supports localized edge states. However, in contrast to the dimer version of the model, a change in the total number of edge states in SSH3 without mirror-symmetry is not necessarily associated with a phase transition, i.e., a closing of the band gap. As such, the topological invariant predicted by the 10-fold way classification does not always coincide with the total number of edge states present. Moreover, although Zak's phase remains quantized for the case of a mirror-symmetric chain, it is known that it fails to take integer values in the absence of this symmetry and thus it cannot play the role of a well-defined bulk invariant in the general case. Attempts to establish a bulk-edge correspondence have been made via Green's functions or through extensions to a synthetic dimension. Here we propose a simple alternative for SSH3, utilizing the previously introduced sublattice Zak's phase, which also remains valid in the absence of mirror symmetry and for noncommensurate chains. The defined bulk quantity…

The recently discovered coexistence of superconductivity and charge-density wave order in the kagome systems $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=\mathrm{K}$, Rb, Cs) has stimulated enormous interest. It is predicted that a vanadium-based kagome system may host a flat band, nontrivial linear dispersive Dirac surface states, and electronic correlation. Although much research has been carried out, the origin of the charge-density wave (CDW) order, the relationship between the superconductivity and the CDW, and whether the anomalous Hall effect (AHE) arises primarily from the kagome lattice or the CDW order, remain controversial. Here, we report an extensive investigation of $\mathrm{Cs}{({\mathrm{V}}_{1\text{\ensuremath{-}}x}{\mathrm{Nb}}_{x})}_{3}{\mathrm{Sb}}_{5}$ samples with systematic Nb doping. Our results show that the Nb doping induces apparent suppression of CDW order and promotes superconductivity; meanwhile, the AHE and magnetoresistance (MR) are weakened significantly together with the CDW order. Combining with density-functional calculations, we interpret these…

The kagome metal compounds $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=\text{K}$, Rb, and Cs) feature a wealth of phenomena including nontrivial band topology, charge density wave (CDW), and superconductivity. One intriguing property is the time-reversal symmetry breaking in the CDW state without local moments, which leads to anomalous transport responses. Here, we report the investigation of magnetothermoelectric effects on high-quality ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ single crystals. A large anomalous Nernst effect (ANE) is observed at temperatures below 30 K and can be enhanced by the high mobility. Multiple Fermi surfaces with small effective masses are revealed by quantum oscillations in the Nernst and Seebeck signals. Furthermore, we discover a magnetic breakdown effect across the two smallest Fermi surfaces, with a gap around 20 meV between them. We propose that the two Fermi surfaces are split from a Dirac band by the CDW gap. These results indicate the large ANE originates from the CDW modulated nontrivial band structure as well as the extrinsic contributions. A second…

A spectral neighbor analysis (SNAP) machine learning interatomic potential (MLIP) has been developed for simulations of carbon at extreme pressures (up to $5\phantom{\rule{0.16em}{0ex}}\mathrm{TPa}$) and temperatures (up to 20 000 K). This was achieved using a large database of experimentally relevant quantum molecular dynamics (QMD) data, training the SNAP potential using a robust machine learning methodology, and performing extensive validation against QMD and experimental data. The resultant carbon MLIP demonstrates unprecedented accuracy and transferability in predicting the carbon phase diagram, melting curves of crystalline phases, and the shock Hugoniot, all within 3% of QMD. By achieving quantum accuracy and efficient implementation on leadership-class high-performance computing systems, SNAP advances frontiers of classical MD simulations by enabling atomic-scale insights at experimental time and length scales.

We present a one-dimensional coupled ring resonator lattice exhibiting a variant of the non-Hermitian skin effect (NHSE) that we call the anomalous Floquet NHSE. Unlike existing approaches to achieving the NHSE by engineering gain and loss on different ring segments, our design uses fixed on-site gain or loss in each ring. The anomalous Floquet NHSE is marked by the existence of skin modes at every value of the Floquet quasienergy, allowing for broadband asymmetric transmission. Varying the gain or loss induces a non-Hermitian topological phase transition, reversing the localization direction of the skin modes. An experimental implementation in an acoustic lattice yields good agreement with theoretical predictions, with a very broad relative bandwidth of around 40%.

Recently, the carbonaceous sulfur hydride was synthesized [E. Snider et al., Nature (London) 586, 373 (2020)], and the measured superconducting transition temperature (${T}_{c}$) is about 278 K under 267 GPa, placing it as a promising candidate of the room temperature superconductor. However, the ultrahigh synthesis pressure is indeed a challenge for experimental technique, stimulating us to search other high temperature superconductors under relatively low pressure. Here we perform comprehensively structural searches of ternary alkaline (Am) boron hydrides. Our calculations indicate that the ternary ${\mathrm{AmB}}_{2}{\mathrm{H}}_{8}$ hydrides are energetically stable at about 10 GPa. Interestingly, the metallic $\mathrm{Rb}/{\mathrm{CsB}}_{2}{\mathrm{H}}_{8}$ polyhydrides are superior superconductors with high ${T}_{c}$ of $\ensuremath{\sim}100$ K at 25 GPa. The electron-phonon coupling calculations suggest that the Am atoms are promising electron contributors, which effectively improve the ${T}_{c}$ and decrease the synthesized pressure in complex hydrides. These findings…

In recent years, charge-two Weyl point phonons (WPPs) have attracted increasing attention. Charge-two WPPs not only provide a new platform for realizing phonon-based unconventional Weyl points (WPs) but also help in realizing specific phonon-based transport behaviors. Herein, based on the first-principles calculations and symmetry analysis, we propose a realistic material with the $P{3}_{1}21$ space group, ${\mathrm{BaZnO}}_{2}$, which has a charge-two WPP and two charge-one WPPs at high-symmetry points. These three unpaired WPPs form a unique triangular Weyl complex. Unlike previously reported material candidates with type-I or type-II charge-two WPPs, the proposed ${\mathrm{BaZnO}}_{2}$ has a type-III charge-two WPP, which has a constant frequency surface that contains two electronlike or holelike states connected at the charge-two WP. ${\mathrm{BaZnO}}_{2}$ can support double-helicoid phonon surface states that cover the entire (001) surface Brillouin zone. The clean type-III WPP, unique triangular Weyl complex, and clear and long surface states in ${\mathrm{BaZnO}}_{2}$ suggest…

We theoretically investigate a nonlinear spin Hall effect in $\mathcal{PT}$-symmetric antiferromagnetic metals, which serve as an efficient spin current generator. We elucidate that an emergent spin-dependent Berry curvature dipole is a microscopic origin of the nonlinear spin Hall effect, which becomes nonzero with neither relativistic spin-orbit coupling, uniform magnetization, nor spin-split band structure. By analyzing a microscopic antiferromagnetic model without spin-orbit coupling for an intuitive understanding of the phenomena, we elucidate essential hopping processes and a condition to enhance the nonlinear spin Hall conductivity. We also provide a complete table to include useful correspondence among the N\'eel vector, odd-parity multipoles, nonlinear spin conductivity tensor, and candidate materials in all the $\mathcal{PT}$-symmetric black-and-white magnetic point groups.

We consider trilayer ${\mathrm{F}}_{1}{\mathrm{F}}_{2}{\mathrm{F}}_{3}$ Josephson junctions that are finite in two dimensions and have arbitrary magnetizations in each ferromagnet ${\mathrm{F}}_{i}\phantom{\rule{0.28em}{0ex}}(i=1,2,3)$. The trilayers are sandwiched between two $s$-wave superconductors with a macroscopic phase difference $\mathrm{\ensuremath{\Delta}}\ensuremath{\varphi}$. Our results reveal that when the magnetizations have three orthogonal components, a supercurrent can flow at $\mathrm{\ensuremath{\Delta}}\ensuremath{\varphi}=0$. With our generalized theoretical and numerical techniques, we study the planar spatial profiles and $\mathrm{\ensuremath{\Delta}}\ensuremath{\varphi}$ dependencies of the charge supercurrents, spin supercurrents, spin torques, and density of states. Remarkably, upon increasing the magnetization strength in the central ferromagnet layer up to the half-metallic limit, the self-biased current and induced second harmonic component become dramatically enhanced while the critical supercurrent reaches its maximum value. Additionally, for a broad…

Quantum many-body scars (QMBS) constitute a new quantum dynamical regime in which rare ``scarred'' eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volume-law for a random bipartition, while scaling for a fine-tuned bipartition is subextensive. When internal symmetries are present, the construction leads to multiple, and even towers, of rainbow scars revealed through distinctive non-thermal dynamics. Remarkably, certain symmetries can lead rainbow scars to arise in translation-invariant models. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydberg-atom quantum simulator, leading to coherent oscillations distinct from the strictly…

We construct a heavy fermion representation for twisted bilayer graphene (TBG) systems. Two local orbitals (per spin/valley) are analytically found, which are exactly the maximally localized zero modes of the continuum Hamiltonian near the AA-stacking center. They have similar properties to the Wannier functions found in a recent study, but also have a clear interpretation as the zeroth pseudo Landau levels (ZLL) of Dirac fermions under the uniform strain field created by twisting. The electronic states of TBG can be viewed as the hybridization between these ZLL orbitals and other itinerant states, which can be obtained following the standard procedure of orthogonalized plane wave method. The ``heavy fermion'' model for TBG separates the strongly correlated components from the itinerant components and provides a solid base for the comprehensive understanding of the exotic physics in TBG.

It is well known that the ground state of homogeneous superconducting systems with spin-orbit coupling in the presence of the Zeeman field is the so-called helical state, which is characterized by the phase modulation of the order parameter, but zero supercurrent density. In this paper we investigate the realization of the helical state in a hybrid system with spatially separated superconductivity and exchange field by considering a superconductor/ferromagnet ($S/F$) bilayer on top of a three-dimensional topological insulator. This system is characterized by strong spin-momentum locking and, consequently, provides the most favorable conditions for the helical state generation. The analysis is based on the microscopic theory in terms of the quasiclassical Green's functions. We demonstrate that in the bilayer the helical state survives if the exchange field has a nonzero component perpendicular to the $S/F$ interface even in spite of the fact that the superconducting order parameter and the exchange field are spatially separated. At the same time, in this spatially inhomogeneous…

Using an effective Dirac model, we study the orbital Hall effect (OHE) in bilayers of transition metal dichalcogenides with 2H stacking (2H-TMD). We use first-order perturbation theory in the interlayer coupling of the bilayer system to obtain analytical expressions for the orbital Hall conductivity in the linear response regime. We use two distinct descriptions of the orbital angular momentum (OAM) operator. The first one is the intra-atomic approximation that considers only the intrasite contribution to the OAM [Cysne et al., Phys. Rev. Lett. 126, 056601 (2021)]. The second one uses the Berry phase formula of the orbital (valley) magnetic moment to describe the OAM operator [Bhowal and Vignale, Phys. Rev. B 103, 195309 (2021)]. This approach includes both intersite and intrasite contributions to the OAM. Our results suggest that the two approaches agree qualitatively in describing the OHE in bilayers of 2H-TMDs, although they present some quantitative differences. We also show that interlayer coupling plays an essential role in understanding the OHE in the unbiased bilayer of…

Multiple-$Q$ magnetic states, such as a skyrmion crystal, become a source of unusual transport phenomena and dynamics. Recent theoretical and experimental studies clarified that such multiple-$Q$ states ubiquitously appear under different crystal structures in metals and insulators. Toward a systematic understanding of the formation of the multiple-$Q$ states in various crystal systems, in this theoretical study we present a low-energy effective spin model with anisotropic exchange interactions in momentum space. We summarize symmetry rules for nonzero symmetric and antisymmetric anisotropic exchange interactions in momentum space, which are regarded as an extension of Moriya's rule. According to the rules, we construct the effective spin model for tetragonal, hexagonal, and trigonal magnets with primitive-lattice and multisublattice structures based on the symmetry of the crystal and wave vector. Furthermore, we describe the microscopic origin of the effective anisotropic exchange interactions in itinerant magnets by perturbatively analyzing a multiband periodic Anderson model with…

In the multiferroic tunnel junction (MFTJ) composed of ferromagnetic and ferroelectric materials, the tunneling electroresistance (TER) coexists with the tunneling magnetoresistance (TMR), making it an ideal platform for designing multifunctional electronic devices. Recently, the rapid development of van der Waals (vdW) materials opened up a new avenue of MFTJ due to their atomic thickness and significance in miniaturizing device sizes. Here by employing the nonequilibrium Green's function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ (FGT)/bilayer $\ensuremath{\alpha}\ensuremath{-}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (BIS)/FGT vdW MFTJs. We find that the MFTJ can form multiple nonvolatile resistance states by altering the polarization orientation of the ferroelectric barrier BIS and the magnetization alignment of the two ferromagnetic FGT electrodes, with a maximum TMR (TER) ratio up to $1.1\ifmmode\times\else\texttimes\fi{}{10}^{7}$% (744%). The TER ratio can be further…

The central issue for practical applications of the anomalous valley Hall effect (AVHE) is the tunable and nonvolatile nature of the valley splitting. We predict a type of ferrovalley material, Janus $1T\ensuremath{-}\mathrm{CrO}X (X=\mathrm{F},\mathrm{Cl},\mathrm{Br},\mathrm{I})$, in which the switching effect of the AVHE can be achieved by adjusting the biaxial strain or building a multiferroic heterostructure $\mathrm{CrO}X/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. Stable out of plane magnetization in $\mathrm{CrO}X$ induces the valley splitting which can reach to 112 meV in the CrOBr monolayer. Interestingly, we find that the valley splitting of CrOCl is robust against the biaxial strain both in the conduction band and the valence band. In contrast, the valley splitting of the CrOBr at the conduction band can be linearly modulated, while it has a switching response at the valence band due to the strong orbital hybridization induced by compressive strain, so a reversible switch of the AVHE can be achieved. Furthermore, the electric reversible valley splitting switch is also obtained…

We studied the magnetic properties of ${\mathrm{YCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Br}}_{2}[{\mathrm{Br}}_{1\ensuremath{-}x}{(\mathrm{OH})}_{x}]$ ($x$ = 0.33), where ${\mathrm{Cu}}^{2+}$ ions form two-dimensional kagome layers. There is no magnetic order down to 50 mK, while the Curie-Weiss temperature is on the order of $\ensuremath{-}100$ K. At zero magnetic field, the low-temperature specific heat shows a ${T}^{2}$ dependence. Above 2 T, a linear temperature dependence term in specific heat emerges, and the value of $\ensuremath{\gamma}=C/T$ increases linearly with the field. Furthermore, the magnetic susceptibility tends to a constant value at $T=0$. Our results suggest that the magnetic ground state of ${\mathrm{YCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Br}}_{2}[{\mathrm{Br}}_{1\ensuremath{-}x}{(\mathrm{OH})}_{x}]$ is consistent with a Dirac quantum-spin-liquid state with a linearly dispersing spinon strongly coupled to an emergent gauge field, which has long been theoretically proposed as a candidate ground state in the two-dimensional kagome Heisenberg antiferromagnetic system.

The collective light-matter interaction in microcavities gives rise to the intriguing phenomena of cavity-mediated transport that can potentially overcome the Anderson localization. Yet, an accurate theoretical treatment is challenging as the matter (e.g., molecules) is subject to large energetic disorder. In this paper, we develop the Green's function solution to the Fano-Anderson model and use the exact analytical solution to quantify the effects of energetic disorder on the spectral and dynamical properties in microcavities. Starting from the microscopic equations of motion, we derive an effective non-Hermitian Hamiltonian and predict a set of scaling laws: (i) The complex eigenenergies of the effective Hamiltonian exhibit an exceptional point, which leads to underdamped coherent dynamics in the weak disorder regime, where the decay rate increases with disorder, and overdamped incoherent dynamics in the strong disorder regime, where the slow decay rate decreases with disorder. (ii) The total density of states of disordered ensembles can be exactly partitioned into the cavity,…

Although topological band theory has been used to discover and classify a wide array of novel topological phases in insulating and semimetal systems, it is not well suited to identifying topological phenomena in metallic or gapless systems. Here, we develop a theory of topological metals based on the system's spectral localizer and associated Clifford pseudospectrum, which can both determine whether a system exhibits boundary-localized states despite the presence of degenerate bulk bands and provide a measure of these states' topological protection even in the absence of a bulk band gap. We demonstrate the generality of this method across symmetry classes in two lattice systems, a Chern metal and a higher-order topological metal, and prove the topology of these systems is robust to relatively strong perturbations. The ability to define invariants for metallic and gapless systems allows for the possibility of finding topological phenomena in a broad range of natural, photonic, and other artificial materials that could not be previously explored.

Cobaltates with $3d$ based layered honeycomb structure were recently proposed as Kitaev magnets and putative candidates to host the long-sought Kitaev spin liquid. Here we present inelastic neutron scattering results down to 50 mK for powder samples of ${\mathrm{Na}}_{3}{\mathrm{Co}}_{2}{\mathrm{SbO}}_{6}$ and ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}{\mathrm{TeO}}_{6}$, with high resolution in regions of low momentum and energy transfers. We compare the experimental data below the antiferromagnetic zigzag ordering temperature with dynamical structure factors obtained within spin wave theory. We search the wide parameter range of a $K\text{\ensuremath{-}}{J}_{1}\text{\ensuremath{-}}\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}{\mathrm{\ensuremath{\Gamma}}}^{\ensuremath{'}}\text{\ensuremath{-}}{J}_{3}$ spin 1/2 model and identify the best fits to constant momentum cuts of the inelastic neutron data. The powder average limits our ability to uniquely select a best-fit model, but we find that the experimental data is matched equally well by two classes of parameters: one with a dominant…

Integer quantum Hall states and their generalization to topological insulators and superconductors are paradigmatic examples of invertible fermionic topological states of matter. Here, the authors develop a comprehensive characterization and classification of invertible fermionic topological phases of matter in two spatial dimensions for general symmetry groups. The results are nonperturbative and apply to strongly interacting systems. In particular, they extend previous classification results to account for the possible chiral nature of invertible phases.

A quantitative description of the excited electronic states of point defects and impurities is crucial for understanding materials properties, and possible applications of defects in quantum technologies. This is a considerable challenge for computational methods, since Kohn-Sham density functional theory (DFT) is inherently a ground-state theory, while higher-level methods are often too computationally expensive for defect systems. Recently, embedding approaches have been applied that treat defect states with many-body methods, while using DFT to describe the bulk host material. We implement such an embedding method, based on Wannierization of defect orbitals and the constrained random-phase approximation approach, and perform systematic characterization of the method for three distinct systems with current technological relevance: a carbon dimer replacing a B and N pair in bulk hexagonal BN (${\mathrm{C}}_{\text{B}}{\mathrm{C}}_{\text{N}}$), the negatively charged nitrogen-vacancy center in diamond (${\mathrm{NV}}^{\ensuremath{-}}$), and an Fe impurity on the Al site in wurtzite…

Multipole symmetries are of interest both as a window on fracton physics and as a crucial ingredient in realizing new universality classes for quantum dynamics. Here we address the question of whether and when multipole symmetries can be spontaneously broken, both in thermal equilibrium and at zero temperature. We derive generalized Mermin-Wagner arguments for the total or partial breaking of multipolar symmetry groups and generalized Imry-Ma arguments for the robustness of such multipolar symmetry breaking to disorder. We present both general results and explicit examples. Our results should be directly applicable to quantum dynamics with multipolar symmetries and also provide a useful stepping stone to understanding the robustness of fracton phases to thermal fluctuations, quantum fluctuations, and disorder.

Generation of entanglement between spatially separated macroscopic systems enables quantum networks and fundamental tests of quantum theory. Here, we propose a scheme to generate a long-range entangled state between two macroscopic spheres. The hybrid system under consideration consists of two massive ferromagnetic spheres and a superconducting transmon qubit, which are both coupled to a microwave cavity array. When the qubit or magnon frequency lies outside of the frequency band of the cavity array, the qubit or magnon mode can seed a tunable, localized cavity mode with an exponentially decaying envelope around its position. This effective cavity mediates the long-range qubit-magnon and magnon-magnon interactions in a coherent way, enabling the long-distance magnon-magnon entanglement via the superconducting qubit.

We revise existing group-theoretical approaches for a treatment of nonrelativistic collinear magnetic systems with perfect translation invariance. We show that full symmetry groups of these systems, which contain elements with independent rotations in the spin and configuration spaces (spin groups), can be replaced by magnetic groups consisting of elements with rotations acting only on position vectors. This reduction follows from modified transformation properties of electron spin, which in the considered systems becomes effectively a pseudoscalar quantity remaining unchanged upon spatial operations but changing its sign due to an operation of antisymmetry. We introduce a unitary representation of the relevant magnetic point groups and use it for a classification of collinear magnets from the viewpoint of antiferromagnetism-induced spin splitting of electron bands near the center of the Brillouin zone. We prove that the recently revealed different altermagnetic classes correspond in a unique way to all nontrivial magnetic Laue classes, i.e., to the Laue groups containing the…

We study 't Hooft anomalies and the related anomaly inflow for subsystem global symmetries. These symmetries and anomalies arise in a number of exotic systems, including models with fracton order such as the $X$-cube model. As is the case for ordinary global symmetries, anomalies for subsystem symmetries can be canceled by anomaly inflow from a bulk theory in one higher dimension; the corresponding bulk is therefore a nontrivial subsystem symmetry protected topological (SSPT) phase. We demonstrate these phenomena in several examples with continuous and discrete subsystem global symmetries, as well as time-reversal symmetry. For each example we describe the boundary anomaly, and present classical continuum actions for the corresponding bulk SSPT phases, which describe the response of background gauge fields associated with the subsystem symmetries. Interestingly, we show that the anomaly does not uniquely specify the bulk SSPT phase. In general, the latter may also depend on how the symmetry and the associated foliation structure on the boundary are extended into the bulk.

Motivated by the recent experimental realizations of hyperbolic lattices in circuit quantum electrodynamics and the research interest in the non-Euclidean generalization of topological phenomena, we investigate the Chern insulator phases in a hyperbolic ${8,3}$ lattice, which is made from regular octagons (8-gons) such that the coordination number of each lattice site is 3. Based on the conformal projection of the hyperbolic lattice into the Euclidean plane, i.e., the Poincar\'e disk model, by calculating the Bott index ($B$) and the two-terminal conductance, we reveal two Chern insulator phases (with $B=1$ and $B=\ensuremath{-}1$, respectively) accompanied by quantized conductance plateaus in the hyperbolic ${8,3}$ lattice. The numerical calculation results of the nonequilibrium local current distribution further confirm that the quantized conductance plateau originates from the chiral edge states and the two Chern insulator phases exhibit opposite chirality. Moreover, we explore the effect of disorder on topological phases in the hyperbolic lattice. It is demonstrated that the…

Recent advances in theory and experiment declare the rare-earth (RE) hydrogen-rich compound $\mathrm{La}{\mathrm{H}}_{10}$ is a near room-temperature superconductor under high pressure. To understand the underlying mechanism of superconductivity and explore the crucial role of lanthanides in forming the RE-based polyhydrides, we here perform a theoretical study on the structural phase transition and superconductivity of late lanthanide ytterbium (Yb) metal under high pressure up to 240 GPa. Two alternative structures, $R\overline{3}m$ and $I4/mmm$ phases, of Yb are presented. Most interestingly, the $P{6}_{3}/mmc$ phase of Yb is serendipitously discovered to be a superior superconductor with a critical temperature value of 19.5 K at 160 GPa, which is higher than other known RE elemental superconductors. The present findings establish an alternative structural phase transition sequence of Yb, which offers insights for further understanding the vital physics mechanisms of a lanthanide-based superconductor.