The 100 most-cited articles in Physical review. B./Physical review. B, 2024

This paper reports angle-resolved photoemission spectroscopy and first-principles band calculations for MnTe, a candidate for an altermagnet that is now emerging as a new type of magnet, distinct from conventional ferromagnets and antiferromagnets. The authors provide direct experimental evidence for an exchange band splitting that reaches 0.8 eV. This band splitting was found to show strong anisotropy and multiple nodal lines in momentum space associated with the PT symmetry breaking characteristic of altermagnets.

We introduce a topological theory to study quasiparticles in interacting and/or disordered many-body systems, which have a finite lifetime due to inelastic and/or elastic scattering. The one-body quasiparticle Hamiltonian includes both the Bloch Hamiltonian of band theory and the self-energy due to interactions, which is non-Hermitian when the quasiparticle lifetime is finite. We study the topology of non-Hermitian quasiparticle Hamiltonians in momentum space, whose energy spectrum is complex. The interplay of band structure and quasiparticle lifetime is found to have remarkable consequences in zero- and small-gap systems. In particular, we predict the existence of topological exceptional points and bulk Fermi arcs in Dirac materials with two distinct quasiparticle lifetimes.

Altermagnets are an unconventional type of magnetic state with various appealing properties, both from the fundamental and applied physics perspectives. By investigating the impact of spin-orbit coupling on these states, this work reveals that all altermagnets are intrinsically noncollinear and that their Zeeman splittings possess symmetry-protected nodal lines. These features endow altermagnets with a remarkable resilience against external magnetic fields.

We study the possibility of superconductivity in a trilayer Ruddlesden-Popper nickelate ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ under pressure both theoretically and experimentally, making comparison with the recently discovered high ${T}_{c}$ superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$, a bilayer nickelate. Through DFT calculations, we find that a structural phase transition from monoclinic to tetragonal takes place around 10--15 GPa. Using the tetragonal crystal structure, we theoretically investigate the possibility of superconductivity, where a combination of fluctuation exchange approximation and linearized Eliashberg equation is applied to a six-orbital model constructed from first-principles band calculations. The obtained results suggests that ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ may also become superconducting under high pressure with ${T}_{c}$ comparable to some cuprates, although it is not as high as ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. We also perform experimental studies using our polycrystalline…

This work describes systematic strongly correlated electronic structure calculations for the candidate double-layer high-temperature superconductor La${}_{3}$Ni${}_{2}$O${}_{7}$ under pressure. These reveal the localized-itinerant duality of Ni ${d}_{{z}^{2}}$ electrons, flat ${d}_{{z}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ quasiparticle bands, and strong interlayer antiferromagnetic correlations due to the interplay of orbital-selective Mott, Hund, and Kondo physics. These results imply a two-component theory with possibly preformed interlayer pairing for the high-temperature superconductivity in pressurized La${}_{3}$Ni${}_{2}$O${}_{7}$. The strange metallicity in the normal state is also explained from the quasiparticle lifetimes.

Recently, altermagnets and superconducting diodes have been garnering a lot of interest, most notably due to their potential for spintronics applications and fundamental physics questions. Here, the authors combine these active fields and demonstrate that altermagnetism can induce superconducting diode behavior in a conventional superconductor, demonstrating that no net magnetic moment is required for this effect. Possible candidates for experimental realization and key characteristics of the effect are also discussed.

Altermagnets feature vanishing net magnetization, similar to antiferromagnets, but exhibit time-reversal symmetry breaking and spin-split band structures. This work constructs minimal models for altermagnetism based on symmetry arguments considering two magnetic atoms in the unit cell and demonstrates that these can capture key properties of the band structure and altermagnetic spin splitting for the material candidate RuO${}_{2}$. Notably, the models have altermagnetic ground states and give rise to a Berry curvature and a conductivity linear in the spin-orbit coupling.

High-${T}_{c}$ superconductivity (SC) has been found experimentally in the bilayer material ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure recently, in which the Ni-$3{d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ and $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals are expected to play a key role in the electronic structure and the SC. Here we study the two-orbital electron correlations and the nature of the SC in the framework of the dynamical mean-field theory using the bilayer two-orbital Hubbard model downfolded from the band structure of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. We find that each of the two orbitals forms ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave SC pairing. Because of the interorbital hoppings, the two-orbital SCs are concomitant, and furthermore they transition to Mott insulating states simultaneously when tuning the system to half filling. The Hund's coupling induced local interorbital spin coupling enhances the electron correlations pronouncedly and is crucial to the SC.

Altermagnetism is increasingly gaining attention and RuO${}_{2}$ thin films have been arguably the most popular altermagnetic candidate. However, most publications miss a disturbing fact: direct experiments indicate the absence of any sizable ordered magnetism in stoichiometric bulk samples. Here, the authors confirm, through first-principles calculations, that the bulk samples are indeed far from ordered magnetism, but intrinsic hole doping strongly enhances the tendency to magnetism, suggesting an interesting possibility that the measured thin films may be magnetically different from stoichiometric bulk RuO${}_{2}$.

Altermagnets are compensated magnets belonging to spin symmetry groups that allow alternating spin polarizations both in the coordinate space of the crystal and in the momentum space of the electronic structure. In these materials the anisotropic local crystal environment of the different sublattices lowers the symmetry of the system so that the opposite-spin sublattices are connected only by rotations. This results in an unconventional spin-polarized band structure in the momentum space. This low symmetry of the crystal structure is expected to be reflected in the anisotropy of the anomalous Hall effect. In this work, we study the anisotropy of the anomalous Hall effect in epitaxial thin films of ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$, an altermagnetic candidate material. We first demonstrate a change in the relative N\'eel vector orientation when rotating the external field orientation through systematic changes in both the anomalous Hall effect and the anisotropic longitudinal magnetoresistance. We then show that the anomalous Hall effect in this material is anisotropic with the…

Altermagnetism, recently spotlighted in condensed matter physics, presents captivating physical properties and holds promise for spintronics applications. This study delves into the theoretical description and categorization of two-dimensional altermagnetism using spin group theory. Employing spin-group formalism, we establish seven distinct spin layer groups, extending beyond the conventional five spin Laue groups, to describe two-dimensional altermagnetism. Utilizing these findings, we classify previously reported two-dimensional altermagnets and identify different materials exhibiting altermagnetism. Specifically, monolayer ${\mathrm{MnTeMoO}}_{6}$ and ${\mathrm{VP}}_{2}{\mathrm{H}}_{8}{({\mathrm{NO}}_{4})}_{2}$ are predicted to be two-dimensional altermagnets. Furthermore, we scrutinize their spin-momentum-locking characteristics through symmetry analysis and density functional theory calculations, substantiating their altermagnetic properties.

Fractionally filled Chern bands with strong interactions may give rise to fractional Chern insulator (FCI) states, the zero-field analog of the fractional quantum Hall effect. Recent experiments have demonstrated the existence of FCIs in twisted bilayer ${\mathrm{MoTe}}_{2}$ without external magnetic fields---most robust at $\ensuremath{\nu}=\ensuremath{-}2/3$---as well as Chern insulators (CIs) at $\ensuremath{\nu}=\ensuremath{-}1$. Although the appearance of both of these states is theoretically natural in an interacting topological system, experiments repeatedly observe nonmagnetic (or weakly magnetic) states (lacking FCIs) at $\ensuremath{\nu}=\ensuremath{-}1/3$ and $\ensuremath{-}4/3$, a puzzling result, which has not been fully theoretically explained. In this paper, we perform Hartree-Fock and exact diagonalization calculations to test whether the standard ${\mathrm{MoTe}}_{2}$ moir\'e model with the (greatly varying) parameter values available in the literature can reproduce the nonmagnetic/weakly magnetic states at $\ensuremath{\nu}=\ensuremath{-}1/3$ and…

The researchers here shed new light on the elusive single-particle model of twisted bilayer MoTe${}_{2}$, a material recently highlighted for hosting fractional Chern insulators at zero magnetic field. By leveraging an advanced machine learning method and density functional theory, the team meticulously maps out the band structure across various twist angles, revealing a pivotal band inversion and refining the theoretical landscape. By enhancing the continuum model with higher harmonic terms, they unveil opposite Chern numbers in the valence bands for key angles, paving the way for predicting diverse Chern states. This comprehensive analysis lays the groundwork for accurately pinpointing correlated phases in this intriguing material, offering a beacon for future explorations.

We explore the possibilities for spin-singlet superconductivity in newly discovered altermagnets. Investigating d -wave altermagnets, we show that finite-momentum superconductivity can easily emerge in altermagnets even though they have no net magnetization, when the superconducting order parameter also has d -wave symmetry with nodes coinciding with the altermagnet nodes. Additionally, we find a rich phase diagram when both altermagnetism and an external magnetic field are considered, including superconductivity appearing at high magnetic fields from a parent zero-field normal state. Published by the American Physical Society 2024

The discovery of superconductivity at 80 K under high pressure in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ presents the groundbreaking confirmation that high-${T}_{c}$ superconductivity is a property of strongly correlated materials beyond cuprates. We use density functional theory calculations of the band structure of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure to verify that the low-energy bands are composed almost exclusively of Ni $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and O $2p$ orbitals. We deduce that the Ni $3{d}_{{z}^{2}}$ orbitals are essentially decoupled by the geometry of the high-pressure structure and by the effect of the Ni Hund coupling being strongly suppressed, which results from the enhanced interlayer antiferromagnetic interaction between $3{d}_{{z}^{2}}$ orbitals and the strong intralayer hybridization of the $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals with O $2p$. By introducing a tight-binding model for the Fermi surfaces and low-energy dispersions, we arrive at a bilayer…

We propose to implement tunable higher-order topological states in a heterojunction consisting of a two-dimensional (2D) topological insulator and the recently discovered altermagnets, whose unique spin-polarization in both real and reciprocal space and null magnetization are in contrast to conventional ferromagnets and antiferromagnets. Based on symmetry analysis and effective edge theory, we show that the special spin splitting in altermagnets with different symmetries, such as $d$ wave, can introduce Dirac mass terms with opposite signs on the adjacent boundaries of the topological insulator, resulting in the higher-order topological state with mass-domain-bound corner states. Moreover, by adjusting the direction of the N\'eel vector, we can manipulate such topological corner states by moving their positions. By first-principles calculations, taking a 2D topological insulator bismuthene with a square lattice on an altermagnet ${\mathrm{MnF}}_{2}$ as an example, we demonstrate the feasibility of creating and manipulating the higher-order topological states through altermagnets.…

In various material systems, an antiferromagnetic phase was found to coexist with a weak ferromagneticlike signal, while symmetry-based theoretical predictions indicate a possibility of a nonzero anomalous Hall effect (AHE) even in the absence of sample magnetization. This is the case of nominally collinear antiferromagnets, in particular, hexagonal MnTe, where the AHE and no detectable magnetization have been recently reported. To clarify the role of magnetization, we present a study of bulk MnTe samples, combining experiment and theory. We demonstrate that the existence of the AHE in the hexagonal MnTe is accompanied by the presence of a weak but detectable ferromagneticlike signal, vanishing at the Néel temperature. In contrast to thin layer samples, we find that the AHE hysteresis loop shows an opposite sign and Barkhausen-like jumps. We introduce a macrospin model involving the Dzyaloshinskii–Moriya type interaction, which explains the existence of a nonzero magnetic moment in the absence of external field and reproduces well hysteretic behavior of the AHE. Using analysis of…

In this paper, we elucidate the formation of bound states in the continuum (BICs) in compound grating waveguide structures from the perspective of momentum mismatch. As the complex lattice reduces to a simple lattice, the excitable guided resonance turns into an unexcitable BIC due to momentum mismatch. Herein, we refer to this state as momentum mismatch driven BIC. Interestingly, as the incidence changes from normal to oblique, the single momentum mismatch driven BIC splits into dual momentum mismatch driven BICs due to the nonzero tangential momentum of the incident light. Distinct from conventional symmetry-protected and accidental BICs, momentum mismatch driven BICs lie in sections of photonic bands. Consequently, factors of momentum mismatch driven quasi-BICs exhibit angular robustness far beyond conventional symmetry-protected and accidental quasi-BICs. Empowered by the momentum mismatch driven BIC, a pair of ellipsometric phase singularities emerge. Enabled by the drastic ellipsometric phase change, ultrasensitive refractive index sensing can be achieved. These results not…

The support of high-$Q$ resonances in all-dielectric nanostructures are necessary for the enhancement of light-matter interactions. By introducing some perturbations into periodic structures to enable an engineered coupling between the supported bound modes and the exterior environment, quasibound modes can consequently be achieved. However, the nature of those modes is still in need of clear investigation. In this work, we employ two geometrically similar binary gratings and demonstrate with both numerical and experimental results that two fundamentally different bound modes may lie behind the high-$Q$ resonances reported in the literature: the bound state in the continuum (BIC) and the guided modes in subwavelength photonic lattices. These two modes have distinct dependences of the $Q$ factor on the wave vector and when they are converted into quasibound (leaky) modes, the same behaviors are retained. We find that only those high-$Q$ resonances with the predecessor of guided modes have robust $Q$ factors over a large range of wave vectors and frequencies, which suggests the high…

In this paper, we propose a concept of bilayer stacking $A$-type altermagnet (BSAA), in which two identical ferromagnetic monolayers are stacked with antiferromagnetic coupling to form a two-dimensional (2D) $A$-type altermagnet. By solving the stacking model, we derive all BSAAs for all layer groups and draw three key conclusions: (i) Only 17 layer groups can realize intrinsic $A$-type altermagnetism. All 2D $A$-type altermagnets must belong to these 17 layer groups, which will be helpful to search for 2D $A$-type altermagnet. (ii) It is impossible to connect the two sublattices of BSAA using ${S}_{3z}$ or ${S}_{6z}$, a constraint that is also applicable to all 2D altermagnets. (iii) ${C}_{2\ensuremath{\alpha}}$ is a general stacking operation to generate BSAA for an arbitrary monolayer. Our theory not only can explain the previously reported twisted-bilayer altermagnets, but also can provide more possibilities to generate $A$-type altermagnets. Our research has significantly broadened the range of candidate materials for 2D altermagnets. Based on conclusion (i), the bilayer…

Photonic bound states in the continuum (BIC) promise a versatile platform for construction of optical resonators with highly confined electromagnetic fields and ultralong radiative lifetime. Merging multiple BIC can enable suppression of out-of-plane radiative losses and further boost the quality (Q) factor of the resonance state. However, current studies on merging BIC (M-BIC) are primarily restricted to the elementary BIC with topological charge $\ifmmode\pm\else\textpm\fi{}1$, which hinders further improvement of the performance of optical resonators. Here, an all-silicon terahertz metasurface (THz-MS) is investigated that supports the symmetry-protected BIC (SP-BIC) with topological charge $\ensuremath{-}2$ and accidental BIC (A-BIC) with topological charge $\ifmmode\pm\else\textpm\fi{}1$ simultaneously. Empowered by the topological nature of BIC, we merge twelve A-BIC with a higher-order SP-BIC at the $\mathrm{\ensuremath{\Gamma}}$ point. By tailoring in-plane mirror symmetry of the THz-MS, we achieve M-BIC at almost arbitrary position in the momentum space. Unlike original…

With recent discoveries of superconductivity in infinite--layer nickelates and in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure, new opportunities appeared that yet another family of high-temperature superconductors based on Ni element may exist in nature, as was previously the case of cuprates and iron-based materials. With their famous strong Coulomb correlations among $3d$ electrons and the proximity to antiferromagnetic instability, these systems represent a challenge for their theoretical description, and most previous studies of superconductivity relied on the solutions of simplified few-orbital model Hamiltonians. Here, on the other hand, we use a recently developed combination of density functional theory with momentum and frequency-resolved self-energies deduced from the so-called fluctuational-exchange--type random phase approximation to study spin fluctuation mediated pairing tendencies in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure. This methodology uses first-principles electronic structures of an actual material and is…

The quantum Mpemba effect is the counterintuitive nonequilibrium phenomenon wherein the dynamic restoration of a broken symmetry occurs more rapidly when the initial state exhibits a higher degree of symmetry breaking. The effect has been recently discovered theoretically and observed experimentally in the framework of global quantum quenches, but so far it has only been investigated in one-dimensional systems. Here we focus on a two-dimensional free-fermion lattice employing the entanglement asymmetry as a measure of symmetry breaking. Our investigation begins with the ground-state analysis of a system featuring nearest-neighbor hoppings and superconducting pairings, the latter breaking explicitly the $\text{U}(1)$ particle-number symmetry. We compute analytically the entanglement asymmetry of a periodic strip using dimensional reduction, an approach that allows us to adjust the extent of the transverse size, achieving a smooth crossover between one and two dimensions. Further applying the same method, we study the time evolution of the entanglement asymmetry after a quench to a…

The search for a novel superconductor exhibiting a high critical temperature (high ${T}_{c}$) or even near room temperature at an accessible synthetic pressure is a persistent objective for both experimental and theoretical physicists. Here, we conduct a systematic high-throughput structure search on boron-carbon clathrates at ambient pressure and uncover two stable 1166-type superconductors, ${\mathrm{RbYbB}}_{6}{\mathrm{C}}_{6}$ and ${\mathrm{RbBaB}}_{6}{\mathrm{C}}_{6}$, both exhibiting maximum ${T}_{c}\ensuremath{\sim}70$ K. The high-${T}_{c}$ superconductivity in 1166-type superconductors is attributed to two key factors: an enhanced density of states at the Fermi level and the strong B-C covalent framework in boron-carbon clathrates, which enhance the electron-phonon coupling and facilitate superconductivity at temperatures near the boiling point of liquid nitrogen. These results provide a significant advancement in understanding the underlying mechanisms of superconductivity in 1166-type boron-carbon based superconductors and offer valuable avenues for the design and…

Understanding the nature of low thermal conductivity and phonon transport properties is critical for the design of potential thermoelectric materials. Based on density-functional theory combined with the phonon Peierls-Boltzmann transport equation, we reveal that Ag-based intercalated layered materials $\mathrm{AgBi}{X}_{2}$ (X = S, Se, and Te) have inherently low lattice thermal conductivity, which is mainly attributed to the anticrossing behavior of low-frequency optical phonons and longitudinal acoustic phonons induced by the rattling mode of the cations. It is found that the optical phonons in $\mathrm{AgBi}{\mathrm{S}}_{2}$ contribute dominantly (up to 65%) to the total thermal conductivity, originating from the weak bonding nature of intercalated Ag atoms that leads to strong anharmonicity and softening of transverse acoustic phonons. Electronic relaxation times under acoustic deformation potential scattering, polar optical phonon scattering, and ionized impurity scattering are considered to obtain reasonable electron transport properties. The ZT value of $p$-type…

Bulk transition metal dichalcogenides (TMDs) have found widespread applications on nanophotonics, condensed matter physics, and quantum optics, due to their high refractive index and stable excitonic response at room temperature. In this paper, based on the finite-element method simulations, we demonstrate that the high refractive index enables the fabrication of bulk $\mathrm{W}{\mathrm{S}}_{2}$ into high-quality-factor metasurfaces that support chiral quasibound states in the continuum (Q-BICs). Interestingly, the Q-BIC resonance can in turn hybridize with excitons in the $\mathrm{W}{\mathrm{S}}_{2}$ metasurface itself. The self-hybridized exciton-polaritons, induced by the strong coupling between a Q-BIC and excitons, exhibit a typical anticrossing behavior with the Rabi splitting up to 136.5 meV. Such remarkable anticrossing behavior is also well elucidated by the coupled oscillator model. Intriguingly, we numerically verify that the self-hybridized exciton-polaritons are photonic spin-controlled, attributed to the chiral Q-BIC with the circular dichroism approaching 0.91.…

We study the Josephson effect in the spin-singlet superconductor/altermagnet/spin-triplet superconductor junctions using the Green's function method. The current-phase difference relationships in the junctions strongly depend on the orientation of altermagnet and the types of the Cooper pairs. For the orientation angle equal to odd multiples of $\ensuremath{\pi}/4$, the current-phase difference relationships are of the $sin2\ensuremath{\phi}$ type, which are irrespective of the pairing wave functions in superconductors. For the other orientation angles, the emergence of the lowest order current becomes possible and its form, $sin\ensuremath{\phi}$ or $cos\ensuremath{\phi}$, depends on the pairing wave functions in superconductors. The ${\ensuremath{\phi}}_{0}$ phase and the $0\text{\ensuremath{-}}\ensuremath{\pi}$ transition can be realized in our junctions due to the appearance of the lowest order current. The selection rules for the lowest order current are presented. The symmetric relations satisfied by the current-phase difference relationships are analyzed through considering…

We study the anomalous Hall effect arising from the altermagnetic order and spin-orbit interaction in doped ${\mathrm{FeSb}}_{2}$. To investigate the anomalous transport, we have constructed a tight-binding model of ${\mathrm{FeSb}}_{2}$. We separately considered the constraints imposed on the model parameters by the spin symmetry group and magnetic symmetry group at zero and finite spin-orbit interaction, respectively. The resulting model includes the effect of exchange splitting and is applicable at both zero and finite spin-orbit interaction. In the case of spin symmetry, the analysis covers the spin-only subgroup arising from collinear magnetism, as well as nontrivial symmetry elements. This allows us to explore changes in the hopping amplitudes as symmetry is reduced by spin-orbit interaction from the spin group to the magnetic group. While the anomalous Hall effect is forbidden by spin symmetry, it is allowed by the symmetries of the magnetic group. The intrinsic Hall conductivity is shown to vanish linearly with spin-orbit interaction. This nonanalytic behavior is universal…

This work systematically investigates the lattice dynamics and phonon thermal transport behavior of the typical negative thermal expansion (NTE) material, cubic ${\mathrm{ScF}}_{3}$. By incorporating thermal expansion, the discrepancy between theoretically predicted and experimentally observed lattice thermal conductivity (${\ensuremath{\kappa}}_{\mathrm{L}}$) is resolved using self-consistent phonon theory, combined with the three- and four-phonon scattering. Our findings reveal that four-phonon interactions significantly increase the ${\ensuremath{\kappa}}_{\mathrm{L}}$ of ${\mathrm{ScF}}_{3}$, which contradicts the traditional intuitive impression that four-phonon interactions suppress thermal transport. This counterintuitive behavior is attributed to the hardening of two rotating phonon modes induced by quartic anharmonicity, suppressing anharmonic scattering and increasing the ${\ensuremath{\kappa}}_{\mathrm{L}}$. Furthermore, we show that thermal expansion enhances anharmonic scattering in ${\mathrm{ScF}}_{3}$, leading to a decrease in ${\ensuremath{\kappa}}_{\mathrm{L}}$.…

Magnetic tunnel junctions (MTJs) are key components of spintronic devices, such as magnetic random-access memories. Normally, MTJs consist of two ferromagnetic (FM) electrodes separated by an insulating barrier layer. Their key functional property is tunneling magnetoresistance (TMR), which is a change in MTJ's resistance when magnetization of the two electrodes alters from parallel to antiparallel. Here, we demonstrate that TMR can occur in MTJs with a single FM electrode, provided that the counterelectrode is an antiferromagnetic (AFM) metal that supports a spin-split band structure and/or a N\'eel spin current. Using $\mathrm{Ru}{\mathrm{O}}_{2}$ as a representative example of such antiferromagnet and $\mathrm{Cr}{\mathrm{O}}_{2}$ as a FM metal, we design all-rutile $\mathrm{Ru}{\mathrm{O}}_{2}/\mathrm{Ti}{\mathrm{O}}_{2}/\mathrm{Cr}{\mathrm{O}}_{2}$ MTJs to reveal a nonvanishing TMR. Our first-principles calculations predict that magnetization reversal in $\mathrm{Cr}{\mathrm{O}}_{2}$ significantly changes conductance of the MTJs stacked in the (110) or (001) planes. The…

The newly discovered altermagnets are unconventional collinear compensated magnetic systems, exhibiting even ($d, g$, or $i$ wave) spin-polarization order in the band structure, setting them apart from conventional collinear ferromagnets and antiferromagnets. Altermagnets offer advantages of spin-polarized current akin to ferromagnets, and THz functionalities similar to antiferromagnets, while introducing new effects like spin-splitter currents. A key challenge for future applications and functionalization of altermagnets is to demonstrate controlled transitioning to the altermagnetic phase from other conventional phases in a single material. Here we prove a viable path toward overcoming this challenge through a strain-induced transition from an antiferromagnetic to an altermagnetic phase in ${\mathrm{ReO}}_{2}$. Combining spin group symmetry analysis and ab initio calculations, we demonstrate that under compressive strain ${\mathrm{ReO}}_{2}$ undergoes such transition, lifting the Kramers degeneracy of the band structure of the antiferromagnetic phase in the nonrelativistic regime.…

A quantum battery (QB) is an energy storage and extraction device that is governed by the principles of quantum mechanics. Here we propose a three-level Dicke QB and investigate its charging process by considering three quantum optical states: a Fock state, a coherent state, and a squeezed state. The performance of the QB in a coherent state is significantly superior to that in a Fock or squeezed state. We show that the locked energy is positively related to the entanglement between the charger and the battery, and diminishing the entanglement increases the ergotropy. The role of quantum phase transitions in the charging process of the QB system is analyzed and we find that the behavior of maximum stored energy is jointly determined by ground and excited-state quantum phase transitions. We further demonstrate that, no matter what the initial state is, the stored energy can be completely extracted when $N$ is small ($N=10$), far below the thermodynamic limit, and the charging power follows a behavior consistent with that of the stored energy.

Altermagnetism, as a new branch of magnetism independent of traditional ferromagnetism and antiferromagnetism, has attracted extensive attention recently. At present, researchers have proved several kinds of three-dimensional altermagnets, but research on two-dimensional (2D) altermagnets remains elusive. Here, we propose a method for designing altermagnetism in 2D lattices: bilayer reversed stacking. This method could enable altermagnetism-type spin splitting to occur intrinsically and the spin splitting could be controlled by crystal chirality. We also demonstrate it through a real material of bilayer $\mathrm{Pt}{\mathrm{Br}}_{3}$ with AB\ensuremath{'} stacking order. Additionally, the combination of stacking order and slidetronics offers opportunities for electrical writing and magnetic reading of electronic devices. In the case of ${\mathrm{AC}}^{\ensuremath{'}}$ stacking, interlayer sliding results in reversible spontaneous polarization. This unique combination of antiferromagnetism and sliding ferroelectricity leads to polarization-controlled spin splitting, thus enabling…

We explore the effect of decoherence on many-body mixed states from a purification perspective. Here, quantum channels map to unitary transformations acting on a purified state defined within an extended Hilbert space. First, we exploit this approach to analyze the phenomenon of spontaneous strong-to-weak symmetry breaking (sw-SSB) triggered by strongly symmetric local quantum channels. We find that sw-SSB for mixed states relates to proximity to a symmetry-protected topological (SPT) order in the purified state. Remarkably, the measurement-induced long-range order in the purified SPT state, as characterized by the R\'enyi-2 correlator, mirrors the ensuing long-range order in the mixed state due to sw-SSB. Moreover, we establish a 1-to-1 correspondence between various sw-SSB order parameters for the mixed state, and strange correlators in the purification, which signify the SPT order. This purification perspective is further extended to explore intrinsic mixed-state topological order and decoherent symmetry-protected topological phases.

We consider phase-biased Josephson junctions with spin-orbit coupling under external magnetic fields and study the emergence of the Josephson diode effect in the presence of Majorana bound states. We show that junctions having middle regions with Zeeman fields along the spin-orbit axis develop a low-energy Andreev spectrum that is asymmetric with respect to the superconducting phase difference ϕ = π , which is strongly influenced by Majorana bound states in the topological phase. This asymmetric Andreev spectrum gives rise to anomalous current-phase curves and critical currents that are different for positive and negative supercurrents, thus signaling the emergence of the Josephson diode effect. While this effect exists even in the trivial phase, it gets enhanced in the topological phase due to the spatial nonlocality of Majorana bound states. Our paper thus establishes the utilization of topological superconductivity for enhancing the functionalities of Josephson diodes. Published by the American Physical Society 2024

We present a general approach for detecting when a fusion category symmetry is anomalous, based on the existence of a special kind of Lagrangian algebra of the corresponding Drinfeld center. The Drinfeld center of a fusion category $\mathcal{A}$ describes a $(2+1)$-dimensional topological order whose gapped boundaries enumerate all $(1+1)$-dimensional gapped phases with the fusion category symmetry, which may be spontaneously broken. There always exists a gapped boundary, given by the electric Lagrangian algebra, that describes a phase with $\mathcal{A}$ fully spontaneously broken. The symmetry defects of this boundary can be identified with the objects in $\mathcal{A}$. We observe that if there exists a different gapped boundary, given by a magnetic Lagrangian algebra, then there exists a gapped phase where $\mathcal{A}$ is not spontaneously broken at all, which means that $\mathcal{A}$ is not anomalous. In certain cases, we show that requiring the existence of such a magnetic Lagrangian algebra leads to highly computable obstructions to $\mathcal{A}$ being anomaly free. As an…

Motivated by high-temperature superconductivity in pressurized ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$, we investigate the pair correlations in the two-orbital Hubbard ladder, which consists of the nearly half-filled and nearly quarter-filled orbitals. By employing the density matrix renormalization group method, we demonstrate that the pair correlation exhibits a power-law decay against the distance while the spin correlation decays exponentially. The decay exponent of the pair correlation of the nearly half-filled orbital is comparable to the exponent of the quasi-long-range superconducting correlation in the doped single-orbital Hubbard ladder, which suggests the importance of the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$.

The field-free and highly efficient diodes with the nonreciprocity of supercurrent are believed to be the core block of superconducting computing devices without dissipation. In this paper, we propose a Josephson diode based upon altermagnets with vanishing net macroscopic magnetization. The nonreciprocity of supercurrent can be realized without applying any external magnetic field or ferromagnetic exchange field, which can avoid the magnetic cross-talk between the basic elements of the devices. A high efficiency exceeding $40%$ can be obtained, and the efficiency shows high stability when the structure parameters are changed. The diode efficiency is antisymmetric about the relative orientation angle of the superconducting leads, so that its sign can easily be inverted by adjusting the relative orientation angle. The symmetries satisfied by the current-phase difference relations and the diode efficiency are analyzed by considering the transformations of the junctions under the time reversal, the spin rotation, and the mirror reflection operations. The high efficiency and the high…

A novel class of antiferromagnets, dubbed altermagnets, exhibit a nonrelativistically spin-split band structure reminiscent of the order parameter phase $d$-wave superconductors, despite the absence of net magnetization. This unique characteristic enables utilization in cryogenic stray-field-free memory devices, offering the possibility of achieving high storage densities. We here determine how a proximate altermagnet influences the critical temperature ${T}_{c}$ of a conventional $s$-wave singlet superconductor. Considering both a bilayer and trilayer, we show that such hybrid structures may serve as stray-field-free memory devices where the critical temperature is controlled by rotating the N\'eel vector of one altermagnet, providing infinite magnetoresistance. Furthermore, our study reveals that altermagnetism can coexist with superconductivity up to a critical strength of the altermagnetic order as well as robustness of the altermagnetic influence on the conduction electrons against nonmagnetic impurities, ensuring the persistence of the proximity effect under realistic…

Exploring spin-valley coupling in two-dimensional (2D) materials with strong spin-orbit coupling (SOC) is of great significance for fundamental physics and practical applications. Using first-principles calculations, we investigate the valley-related properties of Janus $XM{\mathrm{SiN}}_{2}$ $(X=\mathrm{S}, \mathrm{Se}; M=\mathrm{Mo}, \mathrm{Cr})$ monolayer. The Janus $XM{\mathrm{SiN}}_{2}$ monolayer forms a pair of nonequivalent valleys, and the conduction and valence bands are degenerated at the valleys. The inversion symmetry breaking and the SOC effect induce remarkable valley spin splitting and Rashba spin splitting. Our calculations indicate that not only valley-contrasting transport properties but also optical selection rules with spin-valley coupling result in the coexistence of spin and valley Hall effects in the Janus $XM{\mathrm{SiN}}_{2}$ monolayer. Moreover, we demonstrate that the valley-spin physics of the Janus $XM{\mathrm{SiN}}_{2}$ monolayer can be modulated by in-plane biaxial strains, allowing its extraordinary potential for spintronics and valleytronic…

The discovery of high-${T}_{c}$ superconductivity (SC) in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ (LNO) has aroused a great deal of interest. Previously, it was proposed that the Ni-$3{d}_{{z}^{2}}$ orbital is crucial to realize the high-${T}_{c}$ SC in LNO. The preformed Cooper pairs therein acquire coherence via hybridization with the $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital to form the SC. However, we held a different viewpoint that the interlayer pairing $s$-wave SC is induced by the $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital, driven by the strong interlayer superexchange interaction. To include effects from both ${E}_{g}$ orbitals, we establish a two-orbital bilayer $t\text{\ensuremath{-}}J$ model. Our calculations reveal that due to the no-double-occupancy constraint, the $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ band and the $3{d}_{{z}^{2}}$ bonding band are flattened by a factor of about 2 and 10, respectively, which is consistent with recent angle-resolved photoemission spectroscopy measurements. Consequently, a high-temperature SC can be hardly induced in…

The recent discovery of bulk superconductivity in trilayer nickelate ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ under high pressure is attracting a new wave of research interest. In this Letter, we study its electronic band structure and construct a minimal trilayer tight-binding model in terms of the nickel $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and $3{d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbitals, and investigate the superconducting mechanism due to local Coulomb interactions by the unbiased functional renormalization group. We find antiferromagnetic correlations between the outer layers instead of neighboring ones, apart from the in-plane correlations. The effective interaction induces Cooper pairing with the ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave symmetry, which changes sign across the Fermi pockets. In addition, we find the ${T}_{c}$ in ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ is systematically lower than that in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$, but electron doping can further enhance ${T}_{c}$.

In the emerging field of orbitronics, the orbital Hall effect stands out as one of the most important transport phenomena of orbital angular momentum. Here, the authors present a highly efficient and accurate first-principles method to compute the orbital Hall effect by Wannier interpolation and point out the crucial role of the anomalous position for the gauge-covariant description. The work guides the ongoing experimental efforts on the quantitative measurement of orbital currents.

By means of density functional theory plus dynamical mean-field theory, we investigate the correlated electronic structures of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure. Our calculations show that ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ is a multiorbital Hund metal. Both the $3{d}_{{z}^{2}}$ and $3{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals of Ni are close to being half filled and contribute the bands crossing the Fermi level. Band renormalization and orbital selective electronic correlation are observed. Through imaginary-time correlation functions, the discovery of high-spin configuration, spin-frozen phase, and spin-orbital separation shows that the system is in a frozen moment phase at high temperatures above 290 K and is a Fermi liquid at low temperatures, which is further confirmed by the calculated spin, orbital, and charge susceptibilities under high temperatures. Our paper uncovers Hundness in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure.

Circularly polarized lattice vibrations, also known as chiral phonons, carry angular momentum that leads to magnetic response. Recent experiments revealed responses far exceeding prior theoretical predictions within a classical framework. Here, the authors introduce a microscopic model which explains the large magnetic moments of chiral phonons in magnetic materials, resulting from orbit-lattice couplings that hybridize optical phonons with orbital electronic transitions.

Plasmonically induced transparency (PIT) is a physical phenomenon that mimes electromagnetically induced transparency in plasmonic systems. However, it is challenging to maintain its line shape with the presence of disorders or defects, mainly because it is highly susceptible to structural parameters. Herein, a two-dimensional graphene plasmonic system, which is composed of a few periods of vertically arranged graphene-nanoribbon (GNR) pairs coupled with a graphene waveguide, is proposed. By constructing GNRs to form bright and dark plasmon modes with topologically nontrivial phases, the optical response of the graphene waveguide system gives rise to robust PIT effects that exhibit an immunity to a certain degree of various parametric perturbations and imperfections. A three-level plasmonic system is demonstrated to explain the formation mechanism of the PIT effects, and the corresponding results agree well with the numerical ones. Combining topology with PIT helps to reduce the impact of parametric disorders and defects, which benefits the PIT devices with design freedom and higher…

Bound states in the continuum hold extraordinary optical topological properties and can significantly enhance the interaction between light and matter including the circular dichroism (CD) in chiral resonant metasurfaces. In this paper, we demonstrate the split and displacement of topological charges through tilted double-elliptical half-disk metasurfaces. It enables the feasibility to attain perfect intrinsic chiroptic responses, with a CD exceeding 0.99. The ellipticity (\ensuremath{\chi}) of the intrinsic chiroptic response, induced by vertical incidence, is also \ensuremath{\sim}1. In addition to linear chirality CD, significant near-field enhancement contrast is observed at the positions of half-integer topological charge, leading to remarkable nonlinear CD approaching a nearly perfect value of 1. The proposed metasurface simultaneously possesses perfect intrinsic chirality and nonlinear chirality, providing an avenue for the multifaceted development of planar optical devices.

Multiferroic tunnel junctions (MFTJs) have attracted considerable attention due to their multifunctional properties, which are valuable for nonvolatile memory devices. The recent advancements in van der Waals (vdW) multiferroic materials, combining ferromagnetic and ferroelectric properties, provide an excellent platform for exploring MFTJs at the atomic scale. In this study, we employ a combination of nonequilibrium Green's function and density functional theory to theoretically investigate the spin-dependent transport properties of vdW MFTJs, which consist of metal electrodes and sliding multiferroic layered ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$ barrier layers. Our findings demonstrate that asymmetric $\mathrm{Ag}(111)/\text{bilayer}\text{\ensuremath{-}}{\mathrm{VSi}}_{2}{\mathrm{N}}_{4}/\mathrm{Au}(111)$ MFTJs can exhibit multiple nonvolatile resistance states by manipulating the ferroelectric polarization and magnetization alignment of the bilayer ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$, achieving maximum tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) ratios…

As the zero-field analogue of the fractional quantum Hall states, fractional Chern insulator states emerge from topologically nontrivial flat bands realized in lattice systems. Recently, a series of fractionally quantized Hall resistance plateaus have been observed in rhombohedral pentalayer graphene-hBN moir\'e superlattices under zero magnetic field, needing theoretical understanding. The authors have developed a theoretical workflow, discovering both integer and fractional Chern insulator states in rhombohedral multilayer graphene-hBN moir\'e superlattices, which are consistent with recent experimental results.

Remarkable recent experiments have observed fractional quantum anomalous Hall effects at zero field and unusually high temperatures in twisted semiconductor bilayer t MoTe 2 , hence realizing the first genuine fractional Chern insulators. Intriguing observations in these experiments, such as the absence of integer Hall effects at twist angles where a fractional Hall effect is observed, do however remain unexplained. The experimental phase diagram as a function of twist angle remains to be established. By a comprehensive numerical study, including entanglement spectroscopy, we show that band mixing has large qualitative and quantitative effects on the energetics of competing states and their energy gaps throughout the twist angle range θ ≤ 4 ∘ . This lays the foundation for a detailed realistic study of a rich variety of strongly correlated moiré superlattices and an understanding of the phase diagram of these fascinating systems. Published by the American Physical Society 2024

Amidst recent burning interest in quantum anomalous Hall phenomena in pentalayer graphene, the authors provide here an elegant understanding for existing numerical mean field results. Beyond mean field, the authors propose the picture of ``moir\'e-enabled Hall crystals'', emphasizing the crucial role of a moir\'e potential even when weak. The authors provide a connection between electronic crystals and the superconducting Little-Parks effect to explicitly demonstrate the quantization of Chern number associated with spontaneous crystalline order, analogous to quantization of vorticity in a superconducting ring under a background magnetic field.

In this paper, we investigate the relationship between entanglement and nonstabilizerness (also known as magic) in matrix product states (MPSs). We study the relation between magic and the bond dimension used to approximate the ground state of a many-body system in two different contexts: full state of magic and mutual magic (the nonstabilizer analog of mutual information, thus free of boundary effects) of spin-1 anisotropic Heisenberg chains. Our results indicate that obtaining converged results for nonstabilizerness is typically considerably easier than entanglement. For full state magic at critical points and at sufficiently large volumes, we observe convergence with $1/{\ensuremath{\chi}}^{2}$, with $\ensuremath{\chi}$ being the MPS bond dimension. At small volumes, magic saturation is so quick that, within error bars, we cannot appreciate any finite-$\ensuremath{\chi}$ correction. Mutual magic also shows a fast convergence with bond dimension, whose specific functional form is however hindered by sampling errors. As a byproduct of our study, we show how Pauli-Markov chains…

The development of machine-learning interatomic potentials has immensely contributed to the accuracy of simulations of molecules and crystals. However, creating interatomic potentials for magnetic systems that account for both magnetic moments and structural degrees of freedom remains a challenge. This work introduces SpinGNN, a spin-dependent interatomic potential approach that employs the graph neural network (GNN) to describe magnetic systems. SpinGNN consists of two types of edge GNNs: Heisenberg edge GNN (HEGNN) and spin-distance edge GNN (SEGNN). HEGNN is tailored to capture Heisenberg-type spin-lattice interactions, while SEGNN accurately models multibody and high-order spin-lattice coupling. The effectiveness of SpinGNN is demonstrated by its exceptional precision in fitting a high-order spin Hamiltonian and two complex spin-lattice Hamiltonians with great precision. Furthermore, it successfully models the subtle spin-lattice coupling in $\mathrm{BiFe}{\mathrm{O}}_{3}$ and performs large-scale spin-lattice dynamics simulations, predicting its antiferromagnetic ground state,…

The altermagnetism caused by alternating crystal environment provides a unique opportunity for designing new type of valley polarization. Here, we propose a way to realize valley polarization in two-dimensional (2D) tetragonal altermagnetism by regulating the direction of magnetization. The valley polarization along with spin polarization will arise when the orientation of magnetization breaks the ${C}_{4z}$ lattice rotational symmetry, particularly in the conventional in-plane $x$ or $y$ directions. When the direction of magnetization switches between the $x$ and $y$ direction, the valley and spin polarizations will be reversed. This is different from the widely studied valley polarization, which occurs in out-of-plane hexagonal magnetic materials with valley physics at the -K/K point. Followed by first-principles calculations, our proposal is demonstrated in a 2D Janus tetragonal altermagnetic ${\mathrm{Fe}}_{2}{\mathrm{MoS}}_{2}{\mathrm{Se}}_{2}$ monolayer with good stability but very small valley splitting of 1.6 meV. To clearly see the feasibility of our proposal, an…

We carry out a systematic study of the electronic and magnetic structure of the ambient-pressure bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. Employing the hybrid exchange-correlation functional, we show that the exchange correlation pushes the bonding ${d}_{{z}^{2}}$ bands below the Fermi level to be fully occupied. The calculated Fermi surfaces and the correlation normalized band structure match well with the experimental findings at ambient pressure. Moreover, the electronic susceptibility calculated for this band structure features nesting-induced peaks near the wave vector $Q=(\ensuremath{\pi}/2,\ensuremath{\pi}/2)$, suggesting a possible density wave instability in agreement with recent experiments. Through a mean-field study and $\text{DFT}+U$ calculation introducing a Hubbard U interaction within conventional density functional theory, we confirm the spin-charge intertwined double-stripe order is the magnetic ground state. Our results provide a faithful description for the low-pressure ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ electronic structure.

The newly discovered high-${T}_{c}$ nickelate superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ has generated significant research interest. To uncover the pairing mechanism, it is essential to investigate the intriguing interplay between the two ${e}_{g}$, i.e., ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals. Here we conduct an infinite projected entangled-pair state (iPEPS) study of the bilayer $t\text{\ensuremath{-}}J$ model, directly in the thermodynamic limit and with orbitally selective parameters for ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals, respectively. The ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ electrons exhibit significant intralayer hopping ${t}_{\ensuremath{\parallel}}$ (and spin couplings ${J}_{\ensuremath{\parallel}}$) as well as strong interlayer ${J}_{\ensuremath{\perp}}$ passed from the ${d}_{{z}^{2}}$ electrons. However, the interlayer ${t}_{\ensuremath{\perp}}$ is negligible in this case. In contrast, the ${d}_{{z}^{2}}$ orbital demonstrates strong interlayer ${t}_{\ensuremath{\perp}}$ and…

The immense parameter complexity of current neural-network quantum states (NQS) in continuous space renders their application to realistic physical systems impossible. Here, the authors rigorously motivate a many-body coordinate transformation as basis for a variational neural-network Ansatz, implement it via message-passing neural networks, and show a resulting reduction of two orders of magnitude in parameter complexity and convergence speed. With this, the authors open the door for future NQS studies of extended systems in the thermodynamic limit.

Motivated by the recent reports of high-${T}_{c}$ superconductivity in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure, we analyzed theoretically the magnetic excitations in the normal and the superconducting state in this compound, which can be measured by inelastic neutron scattering or resonant inelastic x-ray scattering. We show that the bilayer structure of the spin response allows us to elucidate the role of the interlayer interaction and the nature of the Cooper pairing in a very efficient way. In particular, we demonstrate the key difference between the potential ${s}_{\ifmmode\pm\else\textpm\fi{}}$- and $d$-wave gaps, proposed recently, by comparing the corresponding response in the even and odd channels of the spin susceptibility. We show that the mostly interlayer driven bonding-antibonding ${s}_{\ifmmode\pm\else\textpm\fi{}}$ Cooper pairing produces a single large spin resonance peak in the odd channel only near the $X$ point, whereas spin resonances in both the odd and the even channel are predicted for the $d$-wave scenario.

We study two-dimensional $d$-wave altermagnetic metals, taking into account the presence of substrate-induced Rashba spin-orbit coupling. We consider the altermagnet band structure using a 2D band Hamiltonian near the $\mathrm{\ensuremath{\Gamma}}$ point under external magnetic field. It is shown that time-reversal-symmetry breaking due to altermagnetism, together with Rashba coupling and external magnetic field, can result in nontrivial band topology. The topological phases can be tuned by magnetic field strength and directions, and are classified by their Chern numbers. Furthermore, we investigate the charge response by computing the full optical conductivity tensor with and without magnetic field. In particular, we focus on magneto-optical responses, which are the finite-frequency analog of the Berry curvature-induced anomalous Hall conductivity. Finally, using experimentally realistic parameters for ${\mathrm{RuO}}_{2}$, we estimate the Faraday angle in the absence of magnetic fields.

The observation of fractional Chern insulators in rhombohedral pentalayer graphene twisted on hexagonal boron nitride has initiated a flurry of theoretical work seeking its explanation. As a step towards understanding the origin of these phases, the authors undertake here a first-principles study of the large family of multilayer rhombohedral graphene/boron nitride superlattices, including structural relaxation. The moir\'e models they obtain faithfully capture the microscopic band structure and are the starting point for understanding the observed topological phases and predicting new ones.

We theoretically explore the Josephson diode effect (JDE) in superconductor/quantum dot (QD)/superconductor junction in the presence of a magnetic field and Rashba spin-orbit interaction (RSOI). We calculate the Josephson current in our QD junction using the Keldysh nonequilibrium Green's function technique. We show that JDE is induced in our chiral QD junction with a large rectification coefficient (RC) in the presence of RSOI and external magnetic field simultaneously. Interestingly, the sign and magnitude of the RC are highly controllable by the magnetic field and RSOI. For realistic RSOI strength in the presence of magnetic field and chirality, the RC can be tuned to be as high as $70%$ by an external gate potential, indicating a giant JDE in our QD junction. Our proposed QD-based Josephson diode (JD) may serve as a potential superconducting device component.

The quest for functional materials for the next generation of electronics plays a pivotal role in the postsilicon era, and two-dimensional layered semiconductors are at the core of this extensive research. In this work, we demonstrate that some members of the ${MA}_{2}{Z}_{4}$ family are candidates for high-efficiency optoelectronics. Through first-principles calculations, we find that the intrinsic electron mobility of ${MA}_{2}{\mathrm{N}}_{4}$ (where $M$ = {Mo, W} and $A$ = {Si, Ge}) layer materials reaches up to ${10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ at liquid nitrogen temperature, and decreases as the temperature rises due to the enhanced electron-phonon scattering. Interestingly, the charge transport in these materials takes place purely along the intercalated transition metal nitride layer, so the surface adsorptions (impurities) or substrate interactions have nearly no effect on the carrier mobility due to the $A$-N bilayer protection, and the high electron mobility does not depend on the thickness of the sample.…

Topological band theory has achieved great success in the high-throughput search for topological band structures both in paramagnetic and magnetic crystal materials. However, a significant proportion of materials are topologically trivial insulators at the Fermi level. In this paper, we show that, remarkably, for a subset of the topologically trivial insulators, knowing only their electron number and the Wyckoff positions of the atoms we can separate them into two groups: the obstructed atomic insulator (OAI) and the atomic insulator (AI). The interesting group, the OAI, have a center of charge not localized on the atoms. Using the theory of topological quantum chemistry, in this work we first derive the necessary and sufficient conditions for a topologically trivial insulator to be a filling enforced obstructed atomic insulator (feOAI) in the 1651 Shubnikov space groups. Remarkably, the filling enforced criteria enable the identification of obstructed atomic bands without knowing the representations of the band structures. Hence, no calculations are needed for the filling enforced…

Finite-depth quantum circuits preserve the long-range entanglement structure in quantum states and map between states within a gapped phase. To map between states of different gapped phases, we can use sequential quantum circuits, which apply unitary transformations to local patches, strips, or other subregions of a system in a sequential way. The sequential structure of the circuit, on the one hand, preserves entanglement area law and hence the gappedness of the quantum states. On the other hand, the circuit has generically a linear depth, hence, it is capable of changing the long-range correlation and entanglement of quantum states and the phase they belong to. In this paper, we systematically discuss the definition, basic properties, and prototypical examples of sequential quantum circuits that map product states to Greenberger-Horne-Zeilinger states, symmetry-protected topological states, intrinsic topological states, and fracton states. We discuss the physical interpretation of the power of the circuits through connection to condensation, Kramers-Wannier duality, and the notion…

We investigate the entanglement dynamics of the non-Hermitian Aubry-Andr\'e-Harper chain. The results reveal that by increasing quasiperiodic strength, a phase transition occurs from the area law induced by non-Hermitian skin effect to the area law arising from Anderson localization. For the former, the entanglement entropy follows a nonmonotonic process, i.e., it increases first, then oscillates, and finally converges to a stable value while, for the latter, the entanglement entropy remains low because the wave function is not expandable in Anderson's localization region. The early-stage behavior of entanglement entropy indicates that the two area-law cases are of different phases. Interestingly, the volume-law behavior emerges at the critical point between these two area-law phases. Our study reveals that the area laws induced by the skin effect and the Anderson localization are two different phases, and that a volume law can emerge at the phase transition point. The understanding of the entanglement phase transition induced by disorder and skin effect is thus deepened.

Anomalous Hall crystals (AHCs) form a new phase of matter with spontaneous crystallization and quantized Hall response. It has been invoked to explain a recent experiment on rhombohedral pentalayer graphene, but a simple conceptual understanding of its existence has been lacking. Here, the authors propose a simple three-patch model that captures how quantum mechanical exchange interactions can stabilize the AHC phase, and apply it to analyze the phenomenology of rhombohedral pentalayer graphene.

Recently, the discovery of collinear symmetric-compensated antiferromagnets (AFMs) with intrinsic spin splitting has attracted enormous interest of many researchers. In this paper, we predict the spin-layer coupling in altermagnetic bilayers with tunable spin and valley splitting properties via first-principles calculations. Based on the analysis of magnetic symmetry, we find manipulating magnetic order and stacking configuration as a strategy. Compared with conventional AFM bilayers, the joint symmetry in altermagnetic bilayer can be significantly modulated by different magnetic orders and stackings of the two sublayers. Furthermore, we demonstrate that the layer-dependent spin degeneracy/splitting widely exists in altermagnets with different crystal structures. The spin splitting in an altermagnetic bilayer with various interlayer couplings is highly tunable by external electric field. In contrast with spin splitting introduced by conventional spin-orbit coupling, the concepts of emerging layertronics and altermagnets are combined to manipulate spin properties by spin-layer…

The authors investigate here two bilayer nickelates under pressure, establishing substantial qualitative differences between the two systems. They find that the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital in La${}_{3}$Ni${}_{2}$O${}_{6}$ and La${}_{3}$Ni${}_{2}$O${}_{7}$ plays a different role: one ``active'' orbital (${d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ vs two ``active'' orbitals (${e}_{g})$, respectively. The Fermi surface only has two sheets in La${}_{3}$Ni${}_{2}$O${}_{6}$, with the $\ensuremath{\gamma}$ pocket absent, different from La${}_{3}$Ni${}_{2}$O${}_{7}$. They also find that La${}_{3}$Ni${}_{2}$O${}_{6}$ is far from a superconducting instability. Moreover, they do not observe changes in the electronic density in La${}_{3}$Ni${}_{2}$O${}_{6}$ under pressure.

Large valley polarization and perpendicular magnetocrystalline anisotropy energy (PMAE) in room-temperature ferrovalley materials has been pursued for a long time because PMAE not only stabilizes long-range ferromagnetic (FM) order but also ensures spontaneous valley polarization. Herein, valley polarization and MAE of monolayer $M{X}_{2}$ ($M=\mathrm{Ru},\mathrm{Os}$; $X=\mathrm{Cl},\mathrm{Br}$) are investigated based on first-principles calculations, Wannier functions, and Monte Carlo simulations. It is found that $\mathrm{Os}{\mathrm{Br}}_{2}$ has a giant valley polarization of 327.158 meV and PMAE of 10.354 meV, ascribing to the strong spin-orbital coupling. The physical mechanism of valley polarization and PMAE are analyzed both qualitatively and quantitatively on the basis of perturbation theory, which shows that the valley polarization induces the distribution of MAE at $K$ and ${K}^{\ensuremath{'}}$ valley points with opposite signs, and the couplings between ${d}_{{z}^{2}}$ and ${d}_{yz}, {d}_{xz}$ and ${d}_{xy}$, and ${d}_{{x}^{2}\text{\ensuremath{-}}{y}^{2}}$ and…

The combination of altermagnetism, twistronics, and valleytronics is of great significance for potential applications in advanced electronic devices. Twisted magnetic van der Waals bilayers have been identified as an ideal platform for altermagnetism of any type, such as $d$ wave, $g$ wave, and $i$ wave, by choosing the constituent monolayer with specific symmetry [Y. Liu et al., Phys. Rev. Lett. 133, 206702 (2024)]. Here, we propose a way for achieving valley polarization in twisted altermagnetism by applying an out-of-plane external electric field. Since the out-of-plane electric field creates a layer-dependent electrostatic potential, the valleys from different layers will stagger, producing valley polarization. We also demonstrate the effectiveness of our proposed way using the twisted tight-binding model. It is found that the applied electric field can also induce a valley/spin-gapless semiconductor and half metal besides valley polarization. Based on first-principles calculations, our proposed way to achieve valley polarization can be verified in twisted bilayer VOBr and…

Motivated by exploring correlated multiorbital altermagnets ($\text{A}\ensuremath{\ell}\text{Ms}$) we study minimal $t\ensuremath{-}J$ models on the square-octagon lattice, which favors such a collinear magnetic order. While antiferromagnetic order breaks translational and time-reversal symmetries, the $\text{A}\ensuremath{\ell}\text{M}$ state (equivalently, a ``$d$-wave ferromagnet'') features multipolar order, which separately breaks time-reversal and crystal rotation symmetries but preserves their product leading to spin-split bands with zero net magnetization. We study the mean-field phase diagram of these multiorbital models as we vary doping and interactions, discovering two types of $\text{A}\ensuremath{\ell}\text{M}$ order: (i) itinerant weak-coupling $\text{A}\ensuremath{\ell}\text{M}$ metals driven by quasi-1D van Hove singularities, as well as (ii) strong $\text{A}\ensuremath{\ell}\text{M}$ order at half-filling. We also find regimes of superconductivity including uniform $s$-wave and ${d}_{xy}$-wave pairing states, incipient ${d}_{xy}$-wave pair density wave order, and…

The interplay between the spin-orbit interaction (SOI) and magnetism produces interesting phenomena in superconductors. When a two-dimensional (2D) system with a strong SOI is coupled to an $s$-wave superconductor, an in-plane magnetic field can drive the system into a gapless superconducting state and induce a mirage gap at finite energies for an Ising superconductor. In this Letter, we demonstrate that when an $s$-wave superconductor is proximitized to an altermagnet, the intrinsic anisotropic spin splitting of the altermagnet can result in a gapless superconducting state and a pair of mirage gaps at finite energy. The gapless superconductivity exhibits spin-polarized segmented Fermi surfaces, with coexisting spin-singlet and spin-triplet pairings that have a $d$-wave character. Importantly, the gapless superconducting and mirage gap features are quantified through quantum transport. Our results suggest that the altermagnet is an ideal platform for studying gapless superconducting states and mirage gap physics.

Hydrogen-rich superconductors are promising candidates to achieve room-temperature superconductivity. However, the extreme pressures needed to stabilize these structures significantly limit their practical applications. An effective strategy to reduce the external pressure is to add a light element M that binds with H to form ${\mathrm{MH}}_{x}$ units, acting as a chemical precompressor. We exemplify this idea by performing ab initio calculations of the Ac--Be--H phase diagram, proving that the metallization pressure of Ac--H binaries, for which critical temperatures as high as 200 K were predicted at 200 GPa, can be significantly reduced via beryllium incorporation. We identify three thermodynamically stable (${\mathrm{AcBe}}_{2}{\mathrm{H}}_{10}, {\mathrm{AcBeH}}_{8}$, and ${\mathrm{AcBe}}_{2}{\mathrm{H}}_{14}$) and four metastable compounds (fcc ${\mathrm{AcBeH}}_{8}, {\mathrm{AcBeH}}_{10}, {\mathrm{AcBeH}}_{12}$ and ${\mathrm{AcBe}}_{2}{\mathrm{H}}_{16}$). All of them are superconductors. In particular, fcc ${\mathrm{AcBeH}}_{8}$ remains dynamically stable down to 10 GPa, where…

The authors report here the discovery of a realistic platform for emerging non-Abelian fractional quantum anomalous Hall states. This is the second moir\'e band in 2-degree twisted bilayer MoTe${}_{2}$. They elucidate the theoretical foundation behind this by demonstrating the resemblance of the second moir\'e band to the first Landau level, using Haldane pseudopotentials and Fubini-Study metric. A surprising similarity is revealed between the sequence of moir\'e bands in the twisted bilayer MoTe${}_{2}$ and Landau levels beyond a particular moir\'e band.

Recently, the discovery of superconductivity in Ruddlesden-Popper (RP) ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ under pressure has further expanded the realm of nickelate-based superconductor family. In this paper, we perform a first-principles study of ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ for both the $P{2}_{1}/a$ phase at ambient pressure and $I4/mmm$ phase at high pressure, with $U=0$, 3.5 eV. Our results confirm the characteristic upward shift of a $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ bonding band under pressure. Moreover, our analysis of electronic spectrum and orbital occupancy unveil the dynamic mechanism of electronic reconstructions under pressure, embedded in a critical dual effect. Based on our results, we further propose a trilayer two-orbital model by performing Wannier downfolding on $\mathrm{Ni}\text{\ensuremath{-}}{e}_{g}$ orbitals. Our model reveals four Fermi surface sheets with $\ensuremath{\alpha},\ensuremath{\beta},{\ensuremath{\beta}}^{\ensuremath{'}},\ensuremath{\gamma}$ pockets, bearing resemblance to that of bilayer…

Motivated by the recent experimental breakthroughs in observing fractional quantum anomalous Hall (FQAH) states in moir\'e materials, we propose and study various unconventional phase transitions between quantum Hall phases and Fermi liquids or charge ordered phases upon tuning the bandwidth. At a fixed rational lattice filling $\ensuremath{\nu}$, we describe a quantum Ginzburg-Landau theory to describe the intertwinement between the FQAH and charge density wave (CDW) orders. We use this theory to describe phase transitions between the FQAH and a CDW insulator. The critical theory for a direct second-order transition resembles that of the familiar deconfined quantum critical point (DQCP) but with an additional Chern-Simons term. At filling $\ensuremath{\nu}=\ensuremath{-}1/2$, we study the possibility of a continuous transition between the composite Fermi liquid (CFL) and the Fermi liquid (FL) building on and refining previous work by Barkeshli and McGreevy [Phys. Rev. B 86, 075136 (2012)]. Crucially we show that filling constraints, ignored in that work, ensure that translation…

${\mathrm{TlBiSe}}_{2}$ is considered a potential thermoelectric material due to its ultralow lattice thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{L}}$ and excellent electrical properties. However, previous studies on the thermal properties of ${\mathrm{TlBiSe}}_{2}$ only considered the effects of three-phonon scattering, which resulted in significant differences between theoretical and experimental values. In this material, four-phonon scattering processes mainly reduce the thermal transport of acoustic phonons, resulting in an approximate 28% reduction in particlelike thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{p}}$ at 300 K. The high-frequency optical branches are dense and the phonon lifetime is short, making it easy to generate wavelike phonon tunneling. After considering wavelike thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{c}}$, ${\ensuremath{\kappa}}_{\mathrm{L}}$ along the in-plane direction is in good agreement with the experimental values. A nonstandard ${\ensuremath{\kappa}}_{\mathrm{L}}\ensuremath{\propto}{\mathrm{T}}^{\ensuremath{-}0.36}$…

Conserved-charge densities are very special observables in quantum many-body systems as, by construction, they encode information about the dynamics. Therefore, their evolution is expected to be of much simpler interpretation than that of generic observables and to return universal information on the state of the system at any given time. Here, we study the dynamics of the fluctuations of conserved U ( 1 ) charges in systems that are prepared in charge-asymmetric initial states. We characterize the charge fluctuations in a given subsystem using the full-counting statistics of the truncated charge and the quantum entanglement between the subsystem and the rest resolved to the symmetry sectors of the charge. We show that, even though the initial states considered are homogeneous in space, the charge fluctuations generate an effective inhomogeneity due to the charge-asymmetric nature of the initial states. We use this observation to map the problem into that of charge fluctuations on inhomogeneous, charge-symmetric states and treat it using a recently developed space-time duality…

High temperature superconductivity was recently found in the bilayer nickelate ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ (La327), followed by the discovery of superconductivity in the trilayer ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ (La4310), under high pressure. Through studying the electronic correlation of La4310 with $\mathrm{DFT}+\mathrm{DMFT}$, and further comparing it with that of La327, we find that the ${e}_{g}$ orbitals of the outer-layer Ni cations in La4310 have a similar (but slightly weaker) electronic correlation to those in La327, in which the electrons behave as a non-Fermi liquid with Hund correlation and linear-in-temperature scattering rate. Our results suggest that the experimentally observed ``strange metal'' behavior may be explained by the Hund spin correlation featuring high spin states and spin-orbital separation. In contrast, the electrons in the inner-layer Ni cations in La4310 behave as a Fermi liquid. The weaker electronic correlation in La4310 is attributed to more hole doping, which may explain its lower superconducting…

Altermagnets are compensated magnets with unconventional $d$-, $g$-, and $i$-wave spin order in reciprocal space. So far the search for new altermagnetic candidates has been focused on materials in which the magnetic unit cell is identical to the nonmagnetic one, i.e., magnetic structures with zero propagation vector. Here, we substantially broaden the family of altermagnetic candidates by predicting supercell altermagnets. Their magnetic unit cell is constructed by enlarging the nonmagnetic primitive unit cell, resulting in a nonzero propagation vector for the magnetic structure. This connection of the magnetic configuration to the ordering of sublattices gives an extra degree of freedom to supercell altermagnets, which can allow for the control over the order parameter spatial orientation. We identify realistic candidates ${\mathrm{MnSe}}_{2}$ with a $d$-wave order, and ${\mathrm{RbCoBr}}_{3}, {\mathrm{CsCoCr}}_{3}$, and ${\mathrm{BaMnO}}_{3}$ with $g$-wave order. We demonstrate the reorientation of the order parameter in ${\mathrm{MnSe}}_{2}$, which has two different magnetic…

The electrically nonvolatile control of the easy magnetization axis (EMA) in two-dimensional ferromagnets has attracted significant attention due to its promising applications in spintronic devices. Multiferroic heterostructures, consisting of vertically stacked ferromagnetic and ferroelectric monolayers, have been proposed to manipulate the EMA by reversing the ferroelectric polarization. Here, based on first-principles calculations, we predict a strong magnetoelectric coupling in the multiferroic heterostructure ${\mathrm{EuSn}}_{2}{\mathrm{As}}_{2}/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. Specifically, the EMA of the ferromagnetic monolayer ${\mathrm{EuSn}}_{2}{\mathrm{As}}_{2}$, characterized by a high spin magnetic moment of the rare-earth element Eu, can be switched between in-plane and out-of-plane directions by reversing the polarization direction of the ferroelectric monolayer ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. Our analysis reveals that the polarization direction significantly influences the charge transfer at the interface, introducing band bending, modifying the electronic…

We predict a complete delocalization of the localized states following the localization transition in a one-dimensional non-Hermitian Aubry-Andr\'e model with a generalized quasiperiodic potential. We show that the system first undergoes a transition from the delocalized phase to the localized phase and then to the delocalized phase as a function of the complex phase of the quasiperiodic potential of fixed strength revealing a reentrant delocalization transition. We further identify the localized region as topological in nature exhibiting a well-defined spectral winding number which vanishes in the delocalized phases resulting in a reentrant spectral topological transition. Moreover, we find that these two transitions occur through intermediate regions hosting both delocalized and localized states which also possess nontrivial winding numbers that are different from that of the localized phase.

One of the central questions in condensed matter theory is: can a small Fermi surface phase, which violates the Luttinger theorem, give rise to superconductivity? This paper offers an answer to the question by developing an effective model with the large interlayer exchange coupling ${J}_{\ensuremath{\perp}}$ limit in the bilayer model. The model is dubbed the ESD $t$-$J$ model with six states: one empty state(E), four single states (S), and one double state(D). The authors find that in the normal state with a small doping regime ($x$=0), the small Fermi surface manifests without symmetry breaking or fractionalization, while the conventional Fermi surface appears at the $x$=1 limit. Moreover, the superconducting phase at low temperatures is different from the cuprate. The author predicts a doping-tuned BCS to BEC crossover from Feshbach resonance accompanied by superconducting domes near $x\ensuremath{\sim}0.5$. The theory can be applied to the recently observed high-${T}_{c}$ superconductor La${}_{3}$Ni${}_{2}$O${}_{7}$ under pressure.

Superior to ferromagnetic (FM) materials, antiferromagnetic (AFM) materials do not have any net magnetic moment and are robust to external magnetic perturbation with ultrahigh dynamic speed. To achieve spontaneous valley polarization and anomalous valley Hall effect (AVHE) in AFM materials is of great significance for potential applications in spintronics and valleytronics. Here, we predict an A-type AFM monolayer ${\mathrm{Fe}}_{2}{\mathrm{CF}}_{2}$ with large spontaneous valley polarization. Monolayer ${\mathrm{Fe}}_{2}{\mathrm{CF}}_{2}$ has zero Berry curvature in momentum space but nonzero layer-locked hidden Berry curvature in real space, which provides the basic conditions for the realization of AVHE. Because ${\mathrm{Fe}}_{2}{\mathrm{CF}}_{2}$ possesses the combined symmetry ($PT$ symmetry) of spatial inversion $(P)$ and time reversal $(T)$ symmetry, the spin is degenerate, which prevents the AVHE. An out-of-plane external electric field can be used to produce spin splitting due to the introduction of layer-dependent electrostatic potential, and then layer-locked AVHE can be…

The orbital Hall effect generates a current of orbital angular momentum perpendicular to a charge current. Experiments suggest that this orbital current decays on a long length scale that is of the order of the spin-flip diffusion length or longer. We examine this suggestion using first-principles quantum mechanical scattering calculations to study the decay of orbital currents injected from an orbitally polarized lead into thermally disordered bulk systems of selected transition metals. We find that the decay occurs over only a few atomic layers. On this length scale the orbital current may be converted into a spin current if the spin Hall angle is sufficiently large, as for Pt. In Cu, Cr, and V with small spin Hall angles, the conversion into a spin current is negligible in the bulk and significant conversion only occurs at interfaces.

The mobility edge, as the critical energy separating the extended and localized states, is an important concept in Anderson localization theory. However, how the mobility edge works in non-Hermitian systems has not yet been revealed. Here, through Avila's global theory, the authors prove that the non-Hermitian mobility edge will develop into a ring structure in the complex plane. Combined with numerical calculations, it is convincing that the concept of mobility rings is universal in non-Hermitian quasiperiodic systems.

We propose a method for realizing tunable higher-order topological superconductors (TSCs) by coupling class DIII TSCs with recently discovered altermagnets exhibiting nonrelativistic spin splitting. We exemplify our approach using $d$-wave spin splitting and demonstrate the emergence of inversion-protected Majorana zero modes (MZMs) localized at the corner of the system, i.e., Majorana corner modes. Critically, we show that manipulating the N\'eel vector of the altermagnets enables control over the MZM distribution. This constitutes a crucial step towards achieving non-Abelian braiding of MZMs, a key ingredient for fault-tolerant topological quantum computation. Finally, we discuss a physical system that implements our proposal.

Motivated by the recent observation of superconductivity in the pressurized trilayer Ruddlesden-Popper (RP) nickelate ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$, we explore its structural, electronic, and magnetic properties as a function of hydrostatic pressure from first-principles calculations. We find that an orthorhombic (monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity. The electronic structure of ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ can be understood using a molecular trimer basis wherein $n$ molecular subbands arise as the ${d}_{{z}^{2}}$ orbitals hybridize strongly along the $c$ axis within the trilayer. The magnetic tendencies indicate that the ground state at ambient pressure is formed by nonmagnetic inner planes and stripe-ordered outer planes that are antiferromagnetically coupled along the $c$ axis, resulting in an unusual $\ensuremath{\uparrow}$, 0, $\ensuremath{\downarrow}$ stacking that is consistent with the spin density wave model previously suggested by neutron…

Here we demonstrate the efficient photon-pair generation via spontaneous parametric down conversion from a semiconductor metasurface supporting dual quasibound states in the continuum (quasi-BICs). In a simple metasurface composed of AlGaAs elliptical nanocyclinders, the two high-$Q$ quasi-BIC resonances that coincide with the generated signal and idler frequencies significantly boost the local electric field. This leads to a substantial enhancement in the reverse classical nonlinear process of sum-frequency generation and subsequently the remarkably high generation rate of photon pairs under the quantum-classical correspondence principle. Within a narrowband wavelength regime around the quasi-BIC resonances, the rate of pair production is enhanced up to $\ensuremath{\sim}{10}^{4}$ Hz, two orders of magnitude larger than that in the Mie resonant AlGaAs nanoantennas. Moreover, the photon pair emission is mainly concentrated in the normal direction with respect to the metasurface, and shows a tunable rate with the $Q$ factor by engineering the rotation angle of nanocylinders. The…

Nascent quantum computers motivate the exploration of quantum many-body systems in nontraditional scenarios. For example, it has become natural to explore the dynamics of systems evolving under both unitary evolution and measurement. Such systems can undergo dynamical phase transitions in the entanglement properties of quantum trajectories conditional on the measurement outcomes. Here, we explore dynamics in which one attempts to (locally) use those measurement outcomes to steer the system toward a target state, and we study the resulting phase diagram as a function of the measurement and feedback rates. Steering succeeds when the measurement and feedback rates exceed a threshold, yielding an absorbing-state transition in the trajectory-averaged density matrix. We argue that the absorbing-state transition generally occurs at different critical parameters from the entanglement transition in individual trajectories and has distinct critical properties. The efficacy of steering depends on the nature of the target state: in particular, for local dynamics targeting long-range correlated…

Halide perovskite (HP) materials have recently emerged as a class of semiconductors with immense promise for various optoelectronic applications, ranging from solar cells to light-emitting diodes. One of the unique attributes of HPs is their tunable band gaps with different factors governing their value. The first factor is related to relativistic corrections [``mass-Darwin,'' connected to the $n{s}^{2}$ lone pairs, and spin-orbit coupling (SOC)] that induce an orbital shift or degeneracy splitting, resulting in a band-gap reduction. The second factor involves the structural configuration: in HPs the local symmetry of each Wyckoff position tends to be broken, inducing an opening of the band gap. Based on high-throughput density functional theory calculations, this paper systematically studies a possible self-cancelation on the band-gap correction for HPs when the polymorphous configuration---structural effects---and the SOC---electronic effects---are included. Our results indicate that the nature of interplay between SOC and symmetry breaking (SB) is that they are independent…

In the context of fractional quantum anomalous Hall physics in twisted homobilayer transitional metal dichalcogenides, an emergent magnetic field picture, termed the adiabatic approximation, can be used to explain the emergence of ideal flat bands from the continuum model description. The authors justify here the adiabatic approximation in experimentally relevant parameter regimes and show that the adiabatic approximation is equivalent to an Aharonov-Casher type flat ideal band subject to a periodic potential. Although the potential can significantly modify some properties of the Aharonov-Casher band, its flatness and ideal quantum geometry will be maintained under certain conditions.

Lead zirconate titanate $(\mathrm{PbZ}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{T}{\mathrm{i}}_{x}{\mathrm{O}}_{3},\phantom{\rule{0.16em}{0ex}}\mathrm{PZT})$ exhibits excellent piezoelectric properties in the morphotropic phase boundary (MPB) region of its temperature-composition phase diagram. However, the microscopic origin of its high piezoelectric response remains controversial. Here, we develop a machine-learning-based deep potential (DP) model of PZT using the training data set from first-principles density functional theory calculations. Based on DP-assisted large-scale atomic simulations, we reproduce the temperature-composition phase diagram of PZT, in good agreement with the experiment except for the absence of structural transition from R3c to R3m. We find that the rhombohedral phase maintains R3c symmetry with slight oxygen octahedral tilting with increase of temperature, instead of exhibiting R3m symmetry. This discrepancy could trace back to the lack of experimental measurements to identify such slight octahedral tilting. More importantly, we clarify the atomic-level…

A number of interesting physical phenomena have been discovered in magic-angle twisted bilayer graphene (MATBG), such as superconductivity, correlated gapped and gapless phases, etc. The gapped phases are believed to be symmetry-breaking states described by mean-field theories, whereas gapless phases exhibit features not explained by mean-field theories. This work, using a combination of poor man's scaling, numerical renormalization group, and dynamic mean-field theory, demonstrates that the gapless phases are the heavy-Fermi-liquid state, where some symmetries might be broken while the others are preserved. We adopt the recently proposed topological heavy-fermion model for MATBG, where effective local orbitals around AA-stacking regions and Dirac fermions surrounding them play the roles of local moments (LM's) and itinerant electrons, respectively. At zero temperature and most noninteger fillings, the ground states are found to be heavy Fermi liquids and exhibit Kondo resonance peaks. The Kondo temperature ${T}_{\mathrm{K}}$ is found at the order of 1 meV. A higher temperature than…

The authors provide an analytic theory of the transport of magnetization in a set of interacting anisotropic spin chains. Even though these are many-body systems with diffusive transport on average, the full distribution that gives rise to that average is far from Gaussian -- with fluctuations that, unlike conventional diffusion, are comparable to the mean. This is an example of how systems with the same hydrodynamics can belong to distinct dynamical universality classes.

${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ has garnered widespread interest recently due to its high-temperature superconductivity under pressure, accompanied by charge density wave (CDW) ordering and metal-insulator (MI) transitions in the phase diagram. Here, we explore the nature of CDW and MI transitions using comprehensive first-principles calculations. Our findings reveal that ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ possesses an antiferromagnetic ground state under both low and high pressures, with the strong Fermi surface nesting contributed by the flat band that leads to phonon softening and electronic instabilities. Accordingly, several stable CDW orders with oxygen octahedral distortions are identified. In the presence of apical oxygen vacancies, we identify two different phases exhibiting distortions similar to CDW phases, and their competition can lead to a pressure-induced MI transition. The estimated CDW transition temperature and MI transition pressure agree nicely with experiments. In addition, we find that the electron-phonon coupling is too…

Excitons are neutral excitations that are composed of electrons and holes bound together by their attractive Coulomb interaction. The electron and the hole forming the exciton also interact with the underlying atomic lattice, and this interaction can lead to a trapping potential that favors exciton localization. The quasiparticle thus formed by the exciton and the surrounding lattice distortion is called excitonic polaron. Excitonic polarons have long been thought to exist in a variety of materials, and are often invoked to explain the Stokes shift between the optical absorption edge and the photoluminescence peak. However, quantitative ab initio calculations of these effects are exceedingly rare. In this manuscript, we present a theory of excitonic polarons that is amenable to first-principles calculations. We first apply this theory to model Hamiltonians for Wannier excitons experiencing Fr\"ohlich or Holstein electron-phonon couplings. We find that, in the case of Fr\"ohlich interactions, excitonic polarons only form when there is a significant difference between electron and…

Since the discovery of superconductivity in cuprate materials, the minimal ingredients for high-${T}_{c}$ superconductivity have been an outstanding puzzle. Motivated by the recently discovered nickelate bilayer superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure, we study a minimal bilayer model, in which, as in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$, interlayer and intralayer magnetic interactions but no interlayer hopping are present: A mixed-dimensional (mixD) $t\text{\ensuremath{-}}J$ model. In the setting of a mixD ladder, we show that the system exhibits a crossover associated with a Feshbach resonance: From a closed-channel-dominated regime of tightly bound bosonic pairs of holes to an open-channel-dominated regime of spatially more extended Cooper pairs. The crossover can be tuned by varying doping, or by a nearest-neighbor Coulomb repulsion $V$ that we include in our model. Using density matrix renormalization group simulations and analytical descriptions of both regimes, we find that the ground state is a Luther-Emery liquid,…

Conducting altermagnets have recently emerged as intriguing materials supporting strongly spin-polarized currents without magnetic stray fields. We demonstrate that altermagnets enable three key functionalities, merging superconductivity and spintronics. The first prediction is a controllable supercurrent-induced edge magnetization, which acts like a dissipationless spin-splitter effect. The second and third predictions are a Cooper pair spin-splitter and a filtering effect, respectively. These effects allow for spatial separation of triplet pairs with opposite spin polarizations and spin-selective tunneling of Cooper pairs. We derive a quasiclassical theory with associated boundary conditions that describe these phenomena and explain how they can be experimentally verified. Our results open a new path for spatial control of spin signals via triplet Cooper pairs using hybrid superconductor-altermagnet devices.

Van der Waals multiferroic tunnel junctions (vdW-MFTJs) with multiple nonvolatile resistive states are highly suitable for new physics and next-generation storage electronics. However, currently reported vdW-MFTJs are based on two types of materials, i.e., vdW ferromagnetic and ferroelectric materials, forming a multiferroic system. This undoubtedly introduces additional interfaces, increasing the complexity of experimental preparation. Herein, we engineer vdW intrinsic MFTJs utilizing bilayer ${\mathrm{VS}}_{2}$. By employing the nonequilibrium Green's function combined with density functional theory, we systematically investigate the influence of three types of electrodes (including non-vdW pure metal Ag/Au, vdW metallic $1\mathrm{T}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}/2\mathrm{H}\text{\ensuremath{-}}{\mathrm{PtTe}}_{2}$, and vdW ferromagnetic metallic ${\mathrm{Fe}}_{3}{\mathrm{GaTe}}_{2}/{\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$) on the electronic transport properties of ${\mathrm{VS}}_{2}$-based intrinsic MFTJs. We demonstrate that these MFTJs manifest a giant…