The 100 most-cited articles in Physical review. B./Physical review. B, 2023

For the new high-temperature superconductor La${}_{3}$Ni${}_{2}$O${}_{7}$ under high pressure, the authors analyze its pairing mechanism and pairing symmetry in a bilayer two-orbital Hubbard model. By combining functional renormalization group in weak-to-moderate interaction regime and Gutzwiller approximation for its low-energy effective model projected to atomic one- and two-electron states in the strong-coupling regime, they find robust extended $s$-wave or ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave pairing as triggered by spin fluctuations.

MnTe has recently attracted attention as an altermagnetic candidate. Experimentally it has an altermagnetic order of ferromagnetic $ab$ planes, stacked antiferromagnetically along $c$. We show that this magnetic order (by itself nontrivial, since the in-plane exchange in antiferromagnetic) opens intriguing possibility of manufacturing altermagnetically detwinned samples and generate observable magneto-optical response (which we calculate from first principles) as a signature of altermagnetism.

Topological phases of matter can enable highly stable qubits with small footprints, fast gate times, and digital control. These hardware-protected qubits must be fabricated with a material combination in which a topological phase can reliably be induced. The challenge: disorder can destroy the topological phase and obscure its detection. This paper reports on devices with low enough disorder to pass the topological gap protocol, thereby demonstrating gapped topological superconductivity and paving the way for a new stable qubit.

Motivated by the report of superconductivity in bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ at high pressure, we examine the interacting electrons in this system. First-principles many-body theory is utilized to study the normal-state electronic properties. Below 100 K, a multiorbital non-Fermi-liquid state resulting from a loss of Ni-ligand coherence within a flat-band-dominated low-energy landscape is uncovered. The incoherent low-temperature Fermi surface displays strong mixing between $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ and $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital character. In a model Hamiltonian picture, spin fluctuations originating mostly from the $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ orbital give rise to strong tendencies towards a superconducting instability with a ${B}_{1g}$ or ${B}_{2g}$ order parameter. The dramatic enhancement of ${T}_{\mathrm{c}}$ in pressurized ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ is due to stronger $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ correlations…

Bringing magnetic metals into superconducting states represents an important approach for realizing unconventional superconductors and potentially even topological superconductors. Altermagnetism, classified as a third basic collinear magnetic phase, gives rise to intriguing momentum-dependent spin-splitting of the band structure and results in an even number of spin-polarized Fermi surfaces due to the symmetry-enforced zero net magnetization. In this work, we investigate the effect of this new magnetic order on the superconductivity of a two-dimensional metal with $d$-wave altermagnetism and Rashba spin-orbital coupling. Specifically we consider an extended attractive Hubbard interaction and determine the types of superconducting pairing that can occur in this system and ascertain whether they possess topological properties. Through self-consistent mean-field calculations, we find that the system in general favors a mixture of spin-singlet $s$-wave and spin-triplet $p$-wave pairings and that the altermagnetism is beneficial to the latter. Using symmetry arguments supported by…

The recent discovery of high-${T}_{c}$ superconductivity in bilayer nickelate ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure has stimulated great interest concerning its pairing mechanism. We argue that the weak coupling model from the almost fully filled ${d}_{{z}^{2}}$ bonding band cannot give rise to its high ${T}_{c}$, and thus propose a strong coupling model based on local interlayer spin singlets of Ni-${d}_{{z}^{2}}$ electrons due to their strong on-site Coulomb repulsion. This leads to a minimal effective model that contains local pairing of ${d}_{{z}^{2}}$ electrons and a considerable hybridization with near quarter-filled itinerant ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ electrons on nearest-neighbor sites. Their strong coupling provides a unique two-component scenario to achieve high-${T}_{c}$ superconductivity. Our theory highlights the importance of the bilayer structure of superconducting ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ and points out a potential route for the exploration of more high-${T}_{c}$ superconductors.

The recently discovered high-temperature superconductor La${}_{3}$Ni${}_{2}$O${}_{7\phantom{\rule{0.333em}{0ex}}}$ with ${T}_{c}$ ~ 80 K under pressure has revolutionized the field of correlated electrons. The authors find here that an orbital-selective spin-singlet ``dimer'' linking the two planes of this bilayer via the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital provides the primary building block to study its electronic properties. Furthermore, an in-plane robust interorbital hopping between ${e}_{g}$ states, competes with the more natural intraorbital hopping, leading to a dominant spin stripe ($\ensuremath{\pi}$, 0) order, as well as a rich phase diagram.

Recent works have predicted materials featuring bands with a large spin-splitting distinct from ferromagnetic and relativistically spin-orbit-coupled systems. Materials displaying this property are known as altermagnets and feature a spin-polarized band structure reminiscent of a $d$-wave superconducting order parameter. We here consider the contact between an altermagnet and a superconductor and determine how the altermagnetism affects the fundamental process of Andreev reflection. We show that the resulting charge conductance depends strongly on the interfacial orientation of the altermagnet relative to the superconductor, displaying features similar to normal metals or ferromagnets. The zero-bias conductance peaks present at the interface in the $d$-wave case are robust toward the presence of an altermagnetic interaction. Moreover, the spin conductance also strongly depends on the orientation of the altermagnet relative the interface. These results show how the anisotropic altermagnetic state can be probed by conductance spectroscopy and how it offers voltage control over charge…

The recent observation of the fractional quantum anomalous Hall effect opens a new frontier in topological phases and quantum materials. Here, the authors demonstrate that the strong interaction in partially filled topological moir\'e bands of twisted semiconductor bilayers induces a variety of phases, including ferromagnetic metals, charge density waves, and fractional quantum anomalous Hall states. This work reveals a remarkably rich phase diagram as a function of twist angle, awaiting further exploration.

We propose a minimal toy model for a two-dimensional altermagnet. The model unravels altermagnetic properties at a microscopic level. We find spin-split electron and nondegenerate magnon bands with a $d$-wave symmetry. We use the model to explore magnon-mediated superconductivity in altermagnets. The dominant superconducting state is spin polarized with a $p$-wave symmetry. The state adopts its characteristics from the spin-split electron bands. Furthermore, we find that the superconducting critical temperature of altermagnets can be significantly enhanced by tuning the chemical potential.

Altermagnets are a new class of magnetic materials, which exhibit large spin splitting, but due to the combined spin and real space group symmetry protection maintain zero net macroscopic magnetization. Such a characteristic may prove them to be superior in applications in superconducting heterostructures and thus here we investigate the Andreev reflection at the altermagnet/superconductor interface. We compare and contrast altermagnets to other magnetic materials, revealing qualitative differences in the behavior of altermagnetic junction depending on the Fermi surface orientation. We study the resonant states arising in setups with strong tunneling barriers and show that sensitivity to nonmagnetic disorder is also dependent on the orientation. Our results provide a building block for altermagnetic superconducting heterostructures such as Josephson $\ensuremath{\pi}$ junctions with superior properties.

We predict robust Ising ferromagnetism driven by Coulomb interaction in the metallic phase of twisted transition metal dichalcogenide homobilayers for a range of small twist angles. Due to the presence of spin-valley locking and a Chern band, the completely spin-polarized state---a half metal---has a spin gap and exhibits the anomalous Hall effect. We also find that near a magic angle where the Chern band is predicted to be exceptionally flat, the anomalous Hall metal at $1/3$ filling may become unstable at low temperature and change into a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ charge density wave or a fractional Chern insulator.

80 $K$ superconductivity was recently observed in a La${}_{3}$Ni${}_{2}$O${}_{7}$ under pressure. A pressing challenge is to unravel the intriguing pairing mechanism within these materials. Here, the authors point out a novel role of Hund's rule to transmit the superexchange coupling of the ${d}_{{z}^{2}}$ orbital to the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital, which is a key factor for understanding the remarkably high ${T}_{c}$. The transmitted Hund coupling makes the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital feel a large interlayer spin coupling but no interlayer hopping, a situation not explored before. Within one-orbital mean-field theory, the authors find robust $s$-wave pairing even at 50% hole doping. Moreover, they propose a new analytical framework, the so-called type-II $t$-$J$ model, which they argue is the minimal model to incorporate all essential ingredients, including large Hund's coupling and two orbital effects. This work offers a new model, develops a pioneering method, and identifies intriguing pairing mechanisms in the emerging nickelate field.

We clarify the pairing mechanism of high-${T}_{c}$ superconductivity in bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under high pressure by employing the static auxiliary field Monte Carlo approach to simulate a minimal effective model that contains local ${d}_{{z}^{2}}$ interlayer spin singlets and metallic ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ bands. Superconductivity is induced when the local spin singlet pairs are mobilized and attain long-distance phase coherence by hybridization with the metallic bands. When projected onto realistic Fermi surfaces, it yields a nodeless $s$-wave gap on the $\ensuremath{\gamma}$ Fermi surface, and extended $s$-wave gaps of the same (opposite) sign on the $\ensuremath{\alpha}$ ($\ensuremath{\beta}$) Fermi surface due to its bonding (antibonding) character, with nodes or gap minima along the diagonal direction of the two-dimensional Brillouin zone. We find a dual role of the hybridization that not only induces global phase coherence but also competes with the spin singlet formation. This leads to a tentative phase diagram where…

Fractional Chern insulators exhibit the fractional quantum Hall effect (FQHE) in crystalline systems, without the need for strong magnetic fields, resulting in charge fractionalization, long-range entanglement, and anyonic statistics, potentially at elevated energy scales. The lowest Landau level (LLL) hosts the FQHE, but high Landau levels and many Chern bands do not. Vortexable bands capture the essential physics of the LLL that leads to the FQHE without requiring its more fine-tuned properties, such as uniformity of Berry curvature and of charge density.

We compute the effect of a $d$-wave magnetization (altermagnetism) on the spectrum of bound states (Andreev levels) in a junction between two $s$-wave superconductors (gap ${\mathrm{\ensuremath{\Delta}}}_{0}$ and phase difference $\ensuremath{\phi}$). Compared to a nonmagnetic junction, the $\ensuremath{\phi}$ dependence of the spectrum is shifted by an offset $\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}\ensuremath{\phi}$, dependent on the spin direction, so that the Andreev levels become spin polarized. In a planar junction, oriented along the crystalline axis of ${d}_{xy}$-wave symmetry, the excitation energies are determined by the normal-state transmission probability $T$ according to $E={\mathrm{\ensuremath{\Delta}}}_{0}\sqrt{1\ensuremath{-}T\phantom{\rule{0.16em}{0ex}}{sin}^{2}\frac{1}{2}(\ensuremath{\phi}\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}\ensuremath{\phi})\phantom{{}^{0}}}$. We calculate the corresponding Josephson energy and supercurrent, recovering the 0-$\ensuremath{\pi}$ transition of related studies.

Three mechanisms are known to contribute to second-order nonlinear current: Extrinsic nonlinear Drude, Berry curvature dipole, and intrinsic Berry connection polarizability. Here, we predict an intrinsic contribution to the current related to the quantum metric, a quantum geometric property of the electronic wave function. This contribution manifests in systems that simultaneously break the time-reversal and the inversion symmetry. Interestingly, this contribution is dissipative and contributes to both longitudinal and transverse response. The quantum metric-induced NL current dominates transport in parity-time reversal symmetric systems near the band edges, something we show explicitly for topological antiferromagnets.

Using ab initio band structure and $\mathrm{DFT}+\mathrm{dynamical}$ mean-field theory methods we examine the effects of electron-electron interactions on the normal state electronic structure, Fermi surface, and magnetic correlations of the recently discovered double-layer perovskite superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure. Our results suggest the formation of a negative charge transfer mixed-valence state with the Ni valence close to $1.75+$. We find a remarkable orbital-selective renormalization of the Ni $3d$ bands, with ${m}^{*}/m\ensuremath{\sim}3$ and 2.3 for the Ni $3{z}^{2}\text{\ensuremath{-}}{r}^{2}$ and ${x}^{2}\text{\ensuremath{-}}{y}^{2}$ orbitals, respectively, in agreement with experimental estimates. Our results for the $k$-dependent spectral functions and Fermi surfaces show significant incoherence of the Ni $3{z}^{2}\text{\ensuremath{-}}{r}^{2}$ states, implying the proximity of the Ni $3d$ states to orbital-dependent localization. Based on our analysis of the static magnetic susceptibility, we propose the possible…

We report two nondegenerate magnon modes with opposite spins or chiralities in collinearly antiferromagnetic insulators driven by symmetry-governed anisotropic exchange couplings. The consequent giant spin splitting contributes to spin Seebeck and spin Nernst effects generating longitudinal and transverse spin currents when the temperature gradient applies along and away from the main crystal axis, without requiring any external magnetic field and spin-orbit coupling. Based on first-principle calculations, we predict feasible material candidates holding robust altermagnetic spin configurations to efficiently transport spin. The spin Seebeck conductivity is comparable to the records of antiferromagnets that require the magnetic field, and the spin Nernst conductivity is two orders in magnitude larger than that in antiferromagnetic monolayers that need Berry curvature.

The mutual competition and synergy of magnetism and superconductivity provide us with a very valuable opportunity to access topological superconductivity and Majorana fermions. Here, we devise a heterostructure consisting of an $s$-wave superconductor, a two-dimensional topological insulator, and an altermagnet, which is classified as the third magnet and featured by zero magnetization but spin polarization in both real and reciprocal spaces. We find that the altermagnet can induce mass terms at the edges that compete with electron pairing, and mass domains are formed at the corners of the sample, resulting in zero-energy Majorana corner modes (MCMs). The presence or absence of MCMs can be engineered by only changing the direction of the N\'eel vector. Moreover, uniaxial strain can effectively manipulate the patterns of the MCMs, such as moving and interchanging MCMs. Experimental realization, remarkable advantages of our proposal, and possible braiding are discussed.

Nonstabilizerness, also known as magic, quantifies the number of non-Clifford operations needed to prepare a quantum state. As typical measures either involve minimization procedures or a computational cost exponential in the number of qubits $N$, it is notoriously hard to characterize for many-body states. In this paper, we show that nonstabilizerness, as quantified by the recently introduced stabilizer R\'enyi entropies (SREs), can be computed efficiently for matrix product states (MPSs). Specifically, given an MPS of bond dimension $\ensuremath{\chi}$ and integer R\'enyi index $n>1$, we show that the SRE can be expressed in terms of the norm of an MPS with bond dimension ${\ensuremath{\chi}}^{2n}$. For translation-invariant states, this allows us to extract it from a single tensor, the transfer matrix, while for generic MPSs this construction yields a computational cost linear in $N$ and polynomial in $\ensuremath{\chi}$. We exploit this observation to revisit the study of ground-state nonstabilizerness in the quantum Ising chain, providing accurate numerical results up to large…

Motivated by the recent discovery of superconductivity in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure, we discuss the basic ingredients of a model that captures its microscopic physics under pressure tuning. We anchor our description in terms of the spectroscopic evidence of strong correlations in this system. In a bilayer Hubbard model including the Ni $3d$ ${x}^{2}\ensuremath{-}{y}^{2}$ and ${z}^{2}$ orbitals, we show the ground state of the model crosses over from a low-spin $S=1/2$ state to a high-spin $S=3/2$ state. In the high-spin state, the two ${x}^{2}\ensuremath{-}{y}^{2}$ and the bonding ${z}^{2}$ orbitals are all close to half-filling, which promotes a strong orbital selectivity in a broad crossover regime of the phase diagram pertinent to the system. Based on these results, we construct an effective multiorbital $t\text{\ensuremath{-}}J$ model to describe the superconductivity of the system, and find the leading pairing channel to be an intraorbital spin singlet with a competition between the extended $s$-wave and…

Non-Hermitian quantum many-body systems are attracting widespread interest for their exotic properties, including unconventional quantum criticality and topology. Here, we study how quantum information and correlations spread under a quantum quench generated by a prototypical non-Hermitian spin chain. Using the mapping to fermions, we solve exactly the problem and compute the entanglement entropy and the correlation dynamics in the thermodynamic limit. Depending on the quench parameters, we identify two dynamical phases. One is characterized by rapidly saturating entanglement and correlations. The other presents a logarithmic entanglement growth in time and correlations spreading faster than the associated unitary system, with collapses and revivals giving rise to a modulated light-cone structure. Here, in the long-time limit, we analytically compute the entanglement entropy that follows a logarithmic law, with an effective central charge that we obtain in closed form. Our results provide an example of an exactly solvable non-Hermitian many-body problem that shows rich physics,…

The recent discovery of pressure-induced superconductivity in the bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ (LNO) has opened a new platform for the study of unconventional superconductors. In this publication, we investigate theoretically the whole family of bilayer 327-type nickelates ${R}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ ($R$ = rare-earth elements) under pressure. From La to Lu, the lattice constants and volume decrease, leading to enhanced in-plane and out-of-plane hoppings, resulting in an effectively reduced electronic correlation $U/W$. Furthermore, the Ni's ${t}_{2g}$ states shift away from the ${e}_{g}$ states, while the crystal-field splitting between ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ is almost unchanged. In addition, six candidates were found to become stable in the $Fmmm$ phase, with increasing values of critical pressure as the atomic number increases. Similar to the case of LNO, the ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave pairing tendency dominates in all candidates, due to the nesting between the…

We report and quantify a large orbital-Hall torque generated by Nb and Ru, which we identify from the strong dependence of torques on the ferromagnets. This is manifested as strong enhancement in the dampinglike torques measured in Nb (or Ru)/Ni bilayers as compared to Nb (or Ru)/FeCoB bilayers including the sign reversal in the case of Nb/(Ni or FeCoB) samples. We experimentally observe a striking enhancement of the measured torques with the increase of ferromagnetic Ni thickness which is markedly different from the regular spin-transfer torque; this could be a unique signature of long-range action of the orbital-Hall torques.

The thermal conductivity of monolayer graphene is widely believed to surpass that of diamond even for few-micron-size samples and was proposed to diverge with system size. Here, we predict the thermal conductivity from first principles by considering four-phonon scattering, phonon renormalization, an exact solution to the phonon Boltzmann transport equation (BTE), and a dense enough sampling grid. We show that at room temperature, the thermal conductivity saturates at 10 $\textmu{}\mathrm{m}$ system size and converges to 1300 W/($\mathrm{m}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), which is lower than that of diamond. This indicates that four-phonon scattering overall contributes 57% to the total thermal resistance and becomes the leading phonon scattering mechanism over three-phonon scattering. On the contrary, considering three-phonon scattering only yields higher-than-diamond values and divergence with size due to the momentum-conserving normal processes of flexural phonons.

Most of the H-rich superconductors have so far been discovered to be clathrate structures. Several clathrate hydrides, including ${\mathrm{H}}_{3}\mathrm{S}$, ${\mathrm{LaH}}_{10}$, and ${\mathrm{CaH}}_{6}$, were predicted to be excellent superconductors through structural searches and were later confirmed through experimental synthesis. Here, we conduct extensive crystal structure searches and first-principles calculations for ternary Na-P-H hydrides under high pressure. Two stoichiometries of ${\mathrm{NaPH}}_{6}$ and ${\mathrm{NaPH}}_{8}$ in ternary Na-P-H hydrides are found to be stable under 200 GPa. The $P\overline{6}m2$ phase of the ${\mathrm{NaPH}}_{6}$ hydride is identified as a novel ternary layered H-rich superconductor, exhibiting a high critical temperature ${T}_{c}$ of 112.2 K under 200 GPa. Our calculations indicate that the high ${T}_{c}$ of the ${\mathrm{NaPH}}_{6}$ hydride under high pressure is attributed to the high density of hydrogen $s$ states present at the Fermi level. Furthermore, a metastable $Pm\overline{3}$ phase of the clathrate ${\mathrm{NaPH}}_{6}$…

Currently, designing and exploring a photocatalyst with an interfacial electric field for hydrogen production from water splitting is crucial. Hence, based on first-principles calculations, we first calculate the electronic properties of the two-dimensional hexagonal boron nitride (hBN)/Janus WSSe heterojunction. However, the inherent energy band conformational defects of the hBN/Janus WSSe heterojunction inhibit the efficiency of photocatalytic. To solve this problem, we doped $\mathrm{C}=\mathrm{C}$ bonds on the monolayer hBN to tune the band gap. The research shows that the transition from the traditional type-I band alignment to the type-II band alignment can be achieved through different contracting methods between monolayer hexagonal boron nitride carbon (hBNC) and monolayer Janus WSSe. Notably, the hBNC/SWSe heterojunction is a direct Z-scheme photocatalyst and has high carrier mobility. Compared with the hBNC/SeWS heterojunction, the hBNC/SWSe heterojunction shows higher reduction reaction overpotential…

Cavity optomechanics, a promising platform to investigate macroscopic quantum effects, has been widely used to study nonreciprocal entanglement with the Sagnac effect. Here, we propose an alternative way to realize nonreciprocal entanglement among magnons, photons, and phonons in a hybrid cavity-magnon optomechanics, where the magnon Kerr effect is used. We show that the Kerr effect gives rise to a magnon frequency shift and an additional two-magnon effect. Both of them can be tuned from positive to negative via tuning the magnetic field direction, leading to nonreciprocity. By tuning system parameters such as magnon frequency detuning or the coefficient of the two-magnon effect, bipartite and tripartite entanglements can be nonreciprocally enhanced. By further studying the defined bidirectional contrast ratio, we find that nonreciprocity in our system can be switched on and off, and can be engineered by the bath temperature. Our proposal not only provides a potential path to demonstrate nonreciprocal entanglement with the magnon Kerr effect, but also opens a direction to engineer…

In recent years, it has been shown that Berry curvature monopoles and dipoles play essential roles in the anomalous Hall and the nonlinear Hall effects, respectively. In this work, we demonstrate that Berry curvature multipoles (the higher moments of Berry curvatures at the Fermi energy) can induce higher-order nonlinear anomalous Hall (NLAH) effects. Specifically, an AC Hall voltage perpendicular to the current direction emerges, where the frequency is an integer multiple of the frequency of the applied current. Importantly, by analyzing the symmetry properties of all the 3D and 2D magnetic point groups, we note that the quadrupole, hexapole, and even higher Berry curvature moments can cause the leading-order frequency multiplication in certain materials. To provide concrete examples, we point out that the third-order NLAH voltage can be the leading-order Hall response in certain antiferromagnets due to Berry curvature quadrupoles, and the fourth-order NLAH voltage can be the leading response in the surface states of topological insulators induced by Berry curvature hexapoles. Our…

We present nonlinear optical four-wave mixing in a silicon nanodisk dimer metasurface. Under the oblique incident plane waves, the designed metasurface exhibits a multiresonant feature with simultaneous excitations of three quasi-bound states in the continuum (BIC). Through employing these quasi-BICs with maximizing electric field energy at the input bump wavelengths, significant enhancement of third-order nonlinear processes including third-harmonic generation, degenerate and nondegenerate four-wave mixing are demonstrated, giving rise to ten frequencies in the visible wavelengths. This work may lead to a new frontier of ultracompact optical mixer for applications in optical circuitry, ultrasensitive sensing, and quantum nanophotonics.

The quantum anomalous Hall (QAH) effect is rarely predicted in antiferromagnetic (AFM) materials. Here, by first-principles calculations, we propose that the monolayer of MoO is AFM and can be tuned to be a QAH insulator with a band gap of 50 meV. The MoO monolayer is a tetragonal lattice and we have checked its stability by the phonon spectrum and molecular dynamical simulation. It has a collinear AFM order with magnetic moments larger than $2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ on each Mo atom. In the absence of strain, it is an AFM metal with a direct gap if spin-orbital coupling is considered. Tensile strain results in a metal-insulator phase transition, but it is still topologically trivial protected by an effective time-reversal symmetry. Shear strain breaks this symmetry and leads to the expected nontrivial electronic bands with Chern number $C=\ensuremath{-}1$. In addition, its N\'eel temperature could be larger than room temperature, providing another platform for the application of AFM materials in spintronic devices.

Guided modes in photonic structures, with broadband infinite-quality factors, are inaccessible from the far field due to the momentum mismatch. They become leaky modes in the continuum when the mismatch is compensated for by introducing periodic perturbations to form photonic structures. However, the quality factors (Q factors) of such leaky modes deteriorate significantly in most regions of the $k$-space except at a few discrete high-symmetry points. It is an intriguing question as to whether guided modes can hop above the light cone and yet maintain high Q. Here, we propose a double-band-folding strategy to achieve high-Q leaky modes in compound lattices, exemplified with a one-dimensional grating and a two-dimensional zigzag array of dielectric disks. The Q factor of those leaky modes can be made ultrahigh at arbitrarily any incident angles, showing that such modes do not originate from bound states in the continuum (BICs) above the light cone. Our findings provide unique insight for elucidating the relations between guided modes, BICs, quasi-BICs, and radiation. They further…

We perform a theoretical examination of the local electronic structure in the recently discovered bilayer high-temperature superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. Our method begins with a bilayer two-orbital tight-binding model, incorporating various pairing interaction channels. We determine superconducting order parameters by self-consistently solving the real-space Bogoliubov--de Gennes (BdG) equations, revealing a robust and stable extended $s$-wave pairing symmetry. We investigate the single impurity effect using both self-consistent BdG equations and non-self-consistent $T$-matrix methods, uncovering low-energy in-gap states that can be explained with the $T$-matrix approach. Additionally, we analyze magnetic vortex states using a self-consistent BdG technique, which shows a peak-hump structure in the local density of states at the vortex center. Our results provide identifiable features that can be used to determine the pairing symmetry of the superconducting ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ material.

In 1992, Kennedy and Tasaki constructed a nonlocal unitary transformation that maps between a ${\mathbb{Z}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathbb{Z}}_{2}$ spontaneously symmetry breaking phase and the Haldane gap phase, which is a prototypical symmetry-protected topological (SPT) phase in modern framework, on an open spin chain. In this work, we propose a way to define it on a closed chain by sacrificing unitarity. The operator realizing such a nonunitary transformation satisfies noninvertible fusion rule and implements a generalized gauging of the ${\mathbb{Z}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathbb{Z}}_{2}$ global symmetry. These findings connect the Kennedy-Tasaki transformation to numerous other concepts developed for SPT phases and opens a way to construct SPT phases systematically using the duality mapping.

Symmetry is usually defined via transformations described by a (higher) group. But a symmetry really corresponds to an algebra of local symmetric operators, which directly constrains the properties of the system. In this paper, we point out that the algebra of local symmetric operators contains a special class of extended operators---transparent patch operators, which reveal the selection sectors and hence the corresponding symmetry. The algebra of those transparent patch operators in $n$-dimensional space gives rise to a nondegenerate braided fusion $n$-category, which happens to describe a topological order in one higher dimension (for finite symmetry). Such a holographic theory not only describes (higher) symmetries, it also describes anomalous (higher) symmetries, noninvertible (higher) symmetries (also known as algebraic higher symmetries), and noninvertible gravitational anomalies. Thus, topological order in one higher dimension, replacing group, provides a unified and systematic description of the above generalized symmetries. This is referred to as symmetry/topological-order…

Non-Hermitian systems reveal rich physics beyond the Hermitian regime, and have aroused great interest. One remarkable physical phenomenon is the non-Hermitian skin effect. Recently, topological switching for the non-Hermitian skin effect has been theoretically proposed in cold-atom systems. However, experimental realization of such a phenomenon remains a great challenge. Here, we theoretically propose and experimentally demonstrate a topological switch for the non-Hermitian skin effect in electrical circuit networks. By controlling the operational amplifier and other electric components, the nonreciprocal transport of probability for electrical signals is observed when the switch is turned on. Furthermore, the robustness of such a topological switch is demonstrated both theoretically and experimentally when perturbations are added. Our study provides an avenue for controlling electrical signals in circuit networks, with potential applications in the field of integrated circuit design.

Layer-polarized anomalous Hall effect (LPAHE) is an attractive phenomenon in condensed-matter physics from the standpoints of both fundamental interest and device applications. The current LPAHE research is based on the extrinsic paradigm of using external electric fields, in which the generation and control of LPAHE are not straightforward. Here, we propose a mechanism that realizes intrinsic LPAHE in bilayer lattices, through the mediation of sliding physics and Berry curvature. Moreover, this mechanism can render the LPAHE in a controllable and reversible fashion. We analyze the symmetry requirements for a system to host such intrinsic LPAHE. Its validity is further demonstrated in a real material of bilayer $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$. By stacking with broken inversion symmetry, the layer-locked Berry curvature enables the intrinsic LPAHE in bilayer $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$, and the switchable control of its LPAHE is achieved by sliding ferroelectricity. Our work opens a significant alternative direction for LPAHE and two-dimensional…

Amorphous silicon (a-Si) is an important thermal-management material and also serves as an ideal playground for studying heat transport in strongly disordered materials. Theoretical prediction of the thermal conductivity of a-Si in a wide range of temperatures and sample sizes is still a challenge. Herein we present a systematic investigation of the thermal transport properties of a-Si by employing large-scale molecular dynamics (MD) simulations with an accurate and efficient machine learned neuroevolution potential (NEP) trained against abundant reference data calculated at the quantum-mechanical density-functional-theory level. The high efficiency of NEP allows us to study the effects of finite size and quenching rate in the formation of a-Si in great detail. We find that a simulation cell up to $64\phantom{\rule{0.16em}{0ex}}000$ atoms (a cubic cell with a linear size of 11 nm) and a quenching rate down to ${10}^{11}$ K ${\mathrm{s}}^{\ensuremath{-}1}$ are required for almost convergent thermal conductivity. Structural properties, including short- and medium-range order as…

Our understanding of quantum symmetry of systems has considerably broadened over the last decade. The idea of symmetry has become intrinsically linked with topology described and algebraically characterized by higher categories. Studying three-dimensional systems with noninvertible symmetries, the authors show here that these symmetries are in general incompatible with a unique gapped ground state. Their results extend the ideas behind the Lieb-Shultz-Mattis theorem to the arena of higher-dimensional field theories invariant under a novel class of symmetries.

Located at crystal voids, interstitial anion electrons (IAEs) have diverse topologies, which may be tuned to achieve different properties. Elucidating the role of IAEs in electron-phonon coupling (EPC), and using it to design electride superconductors, leads to the current prediction of superconducting ${\mathrm{Li}}_{8}\mathrm{Au}$ at high pressure. We suggest that the occurence of high-temperature superconductivity in electrides requires high-symmetry structures with hydrogenlike cages, an electron acceptor element to balance charges, and isolated IAEs coupled with medium-frequency vibrations. The uniquely designed ${\mathrm{Li}}_{8}\mathrm{Au}$ electride has a NaCl-type ($B1$) lattice, with atomic Au and cubic ${\mathrm{Li}}_{8}$ cages as bases. Isolated IAEs are formed at the cage centers, with extra charges taken up by Au. These octahedrally coordinated IAEs have a $p$-orbital-like attribute and are strongly coupled with atomic vibrations in the ${\mathrm{Li}}_{8}$ cages. The strong EPC in ${\mathrm{Li}}_{8}\mathrm{Au}$ results in a calculated ${T}_{c}$ of 73.1 K at 250 GPa,…

The emergence of nonrelativistic band spin splitting in fully compensated collinear antiferromagnets provides an intriguing platform for investigating nontrivial spin-dependent phenomena. Here, we explore the relationship between magnetic symmetry and electronic states of two-dimensional (2D) antiferromagnets and demonstrate that nonrelativistic and giant band spin splitting and topological electronic features emerge in room-temperature antiferromagnetic metal ${\mathrm{V}}_{2}{\mathrm{Te}}_{2}\mathrm{O}$ that is sufficiently stable to be exfoliated from the layered compound. More interestingly, the anisotropic spin-momentum coupling of monolayer ${\mathrm{V}}_{2}{\mathrm{Te}}_{2}\mathrm{O}$ gives rise to the spin-Hall effect where the spin-charge conversion ratio is expected to be over 30%, and two fully spin-polarized and separated conduction channels with opposite spin polarization make it an ideal candidate for an electrode that is applied in the antiferromagnetic tunneling junction with large magnetoresistance. Our work elucidates the unexplored potential of 2D…

The sliding ferroelectricity is engineered by artificially stacking the nonpolar two-dimensional (2D) materials, which greatly broadens the 2D ferroelectrics from very few candidate materials to a large family of 2D materials. However, the electric polarizations are generally small due to the weak van der Waals interlayer interaction. The search for 2D sliding ferroelectrics with large polarization presents an ongoing challenge. Here we systematically investigate the sliding ferroelectricity in the bilayer honeycomb structures of $\mathrm{B}X$ $(X=\mathrm{P}, \mathrm{As}, \mathrm{Sb})$, $Y\mathrm{N}$ $(Y=\mathrm{Al}, \mathrm{Ga}, \mathrm{In})$, and $Z\mathrm{C}$ $(Z=\mathrm{Si}, \mathrm{Ge}, \mathrm{Sn})$ based on first-principles calculations. It is shown that the electric polarization decreases with the increase of the interlayer distance, and increases with the difference in electronegativity of the two constituent elements. Such dependence is further corroborated by a simple model. It is interesting to see that GeC can be an ideal sliding ferroelectric material with high…

Two global symmetries are holoequivalent if their algebras of local symmetric operators are isomorphic. A holoequivalent class of global symmetries is described by a topological order (TO) in one higher dimension (called symmetry TO), which leads to a symmetry/topological-order (Symm/TO) correspondence. We establish that (1) for systems with a symmetry described by symmetry TO $\mathcal{M}$, their gapped and gapless states are classified by condensable algebras $\mathcal{A}$, formed by elementary excitations in $\mathcal{M}$ with trivial self-/mutual statistics. These so-called $\mathcal{A}$ states can describe symmetry breaking orders, symmetry protected topological orders, symmetry enriched topological orders, gapless critical points, etc. in a unified way. (2) The local low-energy properties of an $\mathcal{A}$ state can be calculated from its reduced symmetry TO ${\mathcal{M}}_{/\mathcal{A}}$, using holographic modular bootstrap (holoMB) which takes ${\mathcal{M}}_{/\mathcal{A}}$ as an input. Here ${\mathcal{M}}_{/\mathcal{A}}$ is obtained from $\mathcal{M}$ by condensing…

As a paradigm of weak ergodicity breaking in disorder-free nonintegrable models, quantum many-body scars (QMBS) can offer deep insights into the thermalization dynamics of gauge theories. Having been first discovered in a spin-$\frac{1}{2}$ quantum link formulation of the Schwinger model, it is a fundamental question as to whether QMBS persist for $S>\frac{1}{2}$ since such theories converge to the lattice Schwinger model in the large-$S$ limit, which is the appropriate version of lattice QED in one spatial dimension. In this work, we address this question by exploring QMBS in spin-$S\phantom{\rule{4pt}{0ex}}\mathrm{U}(1)$ quantum link models (QLMs) with staggered fermions. We find that QMBS persist at $S>\frac{1}{2}$, with the resonant scarring regime, which occurs for a zero-mass quench, arising from simple high-energy gauge-invariant initial product states. We furthermore find evidence of detuned scarring regimes, which occur for finite-mass quenches starting in the physical vacua and the charge-proliferated state. Our results conclusively show that QMBS exist in a wide class of…

The photonic spin Hall effect (PSHE) plays an important role in both fundamental science and precision metrology. In this paper, we theoretically propose a polarization-dependent bound state in the continuum (BIC) in a compound grating waveguide structure based on the selectable guided resonance at near-infrared wavelengths. Empowered by the unique resonant property and polarization-dependent property of the quasi-BIC, the transverse shift of the PSHE can be intensively enhanced to the order of hundreds of micrometers. Besides, the enhancement of the transverse shift of the PSHE is robust against the geometric parameters. Our work not only provides an all-dielectric platform to achieve giant PSHE, but also offers a viable approach to design high-performance PSHE-based optical devices.

Using first-principles quantum-transport calculations, we investigate spin-dependent electronic and transport properties of antiferromagnetic tunnel junctions (AFMTJs) that consist of (110)-oriented antiferromagnetic (AFM) metal $\mathrm{Ru}{\mathrm{O}}_{2}$ electrodes and an insulating $\mathrm{Ti}{\mathrm{O}}_{2}$ tunneling barrier. We predict the emergence of a giant tunneling magnetoresistance (TMR) effect in a wide energy window, a series of barrier layer thicknesses, and different interface terminations, indicating the robustness of this effect. We show that the predicted TMR cannot be explained in terms of the global transport spin-polarization of $\mathrm{Ru}{\mathrm{O}}_{2}$ (110) but is well understood based on matching the momentum-dependent spin-polarized conduction channels of the two $\mathrm{Ru}{\mathrm{O}}_{2}$ (110) electrodes. We predict oscillations of TMR with increasing barrier thickness, indicating a non-negligible contribution from the perfectly epitaxial interfaces. Our work helps the understanding of the physics of TMR in AFMTJs and aids in realizing…

Superconducting systems that simultaneously lack space-inversion and time-reversal symmetries have recently been the subject of a flurry of experimental and theoretical research activities. Their ability to carry supercurrents with magnitudes depending on the polarity (current direction)---termed the supercurrent diode effect---might be practically exploited to design dissipationless counterparts of contemporary semiconductor-based diodes. Magnetic Josephson junctions realized in the two-dimensional electron gas (2DEG) within a narrow quantum well through proximity to conventional superconductors perhaps belong to the most striking and versatile platforms for such supercurrent rectifiers. Starting from the Bogoliubov--de Gennes approach, we provide a minimal theoretical model to explore the impact of the spin-orbit coupling and magnetic exchange inside the 2DEG on the Andreev bound states and Josephson current-phase relations. Assuming realistic junction parameters, we evaluate the polarity-dependent critical currents to quantify the efficiency of these Josephson junctions as…

The authors investigate here the dynamics of free fermions in a random potential system under continuous monitoring. Repeated measurements are known to induce an entanglement phase transition from a logarithmically entangled critical state to area law, while disorder leads to Anderson localization. They show that their interplay results in a stable critical phase at finite disorder strength and dissipation, which drive a transition consistent with Berezinskii-Kosterlitz-Thouless universality. This work is important for testing such phase transitions in quantum dot arrays and nanowires.

The discovery of strong four-phonon (4ph) interactions in boron arsenide has spurred significant investigations into the influence of higher-order phonon anharmonic scattering on the thermal transport of materials. Considering the special relative regular residual feature and great potential applications in thermoelectrics, this study systematically investigates the anharmonic lattice dynamics and thermal transport behavior of monolayer group-IVB transition metal dichalcogenides $1T\ensuremath{-}M{X}_{2} (M=\mathrm{Ti},\mathrm{Zr},\mathrm{Hf};X=\mathrm{S},\mathrm{Se})$ via ab initio calculations with the self-consistent phonon and Boltzmann transport theories. The calculation results indicate that $1T\ensuremath{-}M{X}_{2}$ has strong 4ph anharmonic scattering and that the phonon dispersion exhibits a significant temperature dependence, which stems from the obvious in-plane quartic potential well vibrations of the transition metal atoms. When 4ph scattering is considered, a remarkable reduction of thermal conductivity is observed in $1T\ensuremath{-}M{X}_{2}$, especially for…

The QSG\ifmmode \hat{W}\else \^{W}\fi{} approximation is presented here. It is an extension to the QSGW formulation [PRB 76, 165106 (2007)] with ladder diagrams in the screening $W$ via the Bethe-Salpeter Equation. Implemented in Questaal (), additional short-ranged correlations in QSG\ifmmode \hat{W}\else \^{W}\fi{} ameliorate much of the discrepancies with experiment for the one-body self-energy and two-body dielectric response in both simple semiconductors and correlated systems such as NiO and CoO, with a stronger effect observed for flat bands.

Simulating collision cascades and radiation damage poses a long-standing challenge for existing interatomic potentials, both in terms of accuracy and efficiency. Machine-learning-based interatomic potentials have shown sufficiently high accuracy for radiation damage simulations, but most existing ones are still not efficient enough to model high-energy collision cascades with sufficiently large space and timescales. To this end, we here extend the highly efficient neuroevolution potential (NEP) framework by combining it with the Ziegler-Biersack-Littmark (ZBL) screened nuclear repulsion potential, obtaining a NEP-ZBL framework. We train a NEP-ZBL model for tungsten and demonstrate its accuracy in terms of the elastic properties, melting point, and various energetics of defects that are relevant for radiation damage. We then perform large-scale molecular dynamics simulations with the NEP-ZBL model with up to 8.1 million atoms and 240 ps (using a single 40-GB A100 GPU) to study the difference of primary radiation damage in both bulk and thin-foil tungsten. While our findings for bulk…

${\mathrm{GdRu}}_{2}{\mathrm{Si}}_{2}$ is a centrosymmetric magnet in which a skyrmion lattice has recently been discovered. Here, we investigate the magnetic structure of the zero-field ground state using neutron diffraction on single crystal and polycrystalline ${^{160}\mathrm{GdRu}}_{2}{\mathrm{Si}}_{2}$. In addition to observing the principal propagation vectors ${\mathbf{q}}_{1}$ and ${\mathbf{q}}_{2}$, we discover higher-order magnetic satellites, notably ${\mathbf{q}}_{1}+2{\mathbf{q}}_{2}$. The appearance of these satellites is explained within the framework of a double-$Q$ constant-moment solution. Using powder diffraction, we implement a quantitative refinement of this model. This structure, which contains vortexlike motifs, is shown to have a one-dimensional topological charge density.

In condensed matter physics, materials with kagome lattice display a range of exotic quantum states, including charge density wave (CDW), superconductivity, and magnetism. Recently, the intermetallic kagome metal ${\mathrm{ScV}}_{6}{\mathrm{Sn}}_{6}$ was discovered to undergo a first-order structural phase transition with the formation of a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ifmmode\times\else\texttimes\fi{}3$ CDW at around 92 K. The bulk electronic band properties are crucial to understanding the origin of the structural phase transition. Here, we conducted an optical spectroscopy study in combination with band structure calculations across the structural transition. Our findings showed abrupt changes in the optical reflectivity/conductivity spectra as a result of the structural transition, without any observable gap formation behavior. The optical measurements and band calculations actually reveal a sudden change of the band structure after transition. It is important to note that this phase transition is of the first-order type, which distinguishes it from…

Two-dimensional (2D) Janus materials due to their asymmetric structures show fascinating spintronic and piezoelectric properties making them a research hot spot in recent years. In this work, inspired by Janus group-III monochalcogenides, we propose $\mathrm{Zn}AXY$ ($A=\mathrm{Si}$, Ge, Sn, and $X/Y=\mathrm{S}$, Se, Te, $X

On the basis of the self-consistent phonon theory and the special displacement method, we develop an approach for the treatment of anharmonicity in solids. We show that this approach enables the efficient calculation of temperature-dependent anharmonic phonon dispersions, requiring very few steps to achieve minimization of the system's free energy. We demonstrate this methodology in the regime of strongly anharmonic materials, which exhibit a multiwell potential energy surface, like cubic ${\mathrm{SrTiO}}_{3}$, ${\mathrm{CsPbBr}}_{3}$, ${\mathrm{CsPbI}}_{3}$, ${\mathrm{CsSnI}}_{3}$, and Zr. Our results are in good agreement with experiments and previous first-principles studies relying on stochastic nonperturbative and molecular dynamics simulations. We achieve a very robust workflow by using harmonic phonons of the polymorphous ground state as the starting point and an iterative mixing scheme of the dynamical matrix. We also suggest that the phonons of the polymorphous ground state might provide an excellent starting approximation to explore anharmonicity. Given the simplicity,…

Quantum many-body scars (QMBSs) are a paradigm of weak ergodicity breaking with direct technological applications. The authors show that QMBSs are ubiquitous in quantum link formulations of gauge theories, opening the door to a large venue of models where QMBSs can be explored. They demonstrate that QMBSs are not an artifact of these quantum link formulations, rather, they may be an inherent feature of the ideal gauge theory itself.

Lightly doped multilayer graphene surprised researchers with the emergence of superconductivity and magnetism under strong electric displacement fields. The authors interpret the displacement field versus hole-density phase diagram using mean-field theory and experimentally informed band structure. They find that magnetism in these electronic systems is often intertwined with nematic order because of the noncompact Fermi sea topology and fourfold spin-valley degeneracy.

Inelastic neutron scattering provides a powerful probe of the magnetic excitations of quantum magnets. Altermagnets have recently emerged as a new class of magnets with vanishing net magnetization characteristic of antiferromagnets and with a spin-split electronic structure typical of ferromagnets. Here we introduce a minimal Hubbard model with two-sublattice orthorhombic anisotropy as a framework to study altermagnetism. Using unrestricted Hartree-Fock calculations, we find an altermagnetic state for this model that evolves from a metallic state to an insulating state with increasing Hubbard-$U$ Coulomb repulsion. We then examine the inelastic neutron scattering response in these states using random-phase approximation calculations of the dynamic spin susceptibility ${\ensuremath{\chi}}^{\ensuremath{''}}(\mathbf{q},\ensuremath{\omega})$. We find that the magnetic excitation spectrum depends on its chirality for $\mathbf{q}$ along certain directions in reciprocal space, an observation that may be used in inelastic neutron scattering experiments as a probe of altermagnetism.

Silicon/silicon-germanium heterostructures have many important advantages for hosting spin qubits. However, controlling the valley splitting (the energy splitting between the two low-lying conduction-band valleys) remains a critical challenge for ensuring qubit reliability. Broad distributions of valley splittings are commonplace, even among quantum dots formed on the same chip. In this work, we theoretically explore the interplay between quantum-well imperfections that suppress the valley splitting and cause variability, such as broadened interfaces and atomic steps at the interface, while self-consistently accounting for germanium concentration fluctuations. We consider both conventional and unconventional approaches for controlling the valley splitting and present concrete strategies for implementing them. Our results provide a clear path for achieving qubit uniformity in a scalable silicon quantum computer.

Photonic crystals (PhCs) have emerged as a popular platform for realizing various topological phases due to their flexibility and potential for device applications. In this article, we present a comprehensive classification of topological bands in one- and two-dimensional photonic crystals, with and without time-reversal symmetry. Our approach exploits the symmetry representations of field eigenmodes at high-symmetry points in momentum space, allowing for the efficient design of a wide range of topological PhCs. In particular, we show that the complete classification provided here is useful for diagnosing photonic crystal analogs of obstructed atomic limits, fragile phases, and stable topological phases that include bands with Dirac points and Chern numbers.

We investigate the influence of three- and four-phonon scattering, perturbative anharmonic phonon renormalization, and off-diagonal terms of coherent phonons on the thermal conductivity of ${\mathrm{CsPbBr}}_{3}$ phase change perovskite, by using advanced implementations and first-principles simulations. Our study spans a wide temperature range covering the entire structural spectrum. Notably, we demonstrate that the interactions between acoustic and optical phonons result in contrasting trends of phonon frequency shifts for the high-lying optical phonons in orthorhombic and cubic ${\mathrm{CsPbBr}}_{3}$ as temperature varies. Our findings highlight the significance of wavelike tunneling of coherent phonons in ultralow and glasslike thermal conductivity in halide perovskites.

Systems with local non-Hermiticity are beyond the scope of both Bloch and non-Bloch band descriptions. Here, the authors establish a new paradigm for such systems: the emergence of scale-free localized states induced by local non-Hermiticity. They demonstrate that the scale-free localization is a generic phenomenon, regardless of the parity-time symmetry, the eigenstates' coalescence, or even the incommensurate disorder. The results also indicate that the bulk properties of the original Hermitian systems can be globally reshaped by local non-Hermiticity.

Two-dimensional (2D) ferroelectric materials have attracted great attention in recent years due to their thin thickness, high stability, and switchable polarization states. In particular, ferroelectric tunnel junctions (FTJs) constructed from 2D ferroelectric materials have been shown to have very high tunnel electroresistance (TER) ratios. In this work, we design a ferroelectric tunnel junction composed of ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ vertical van der Waals (vdW) heterostructure based on two different 2D ferroelectric materials with out-of-plane polarization. Through density functional calculations combined with a nonequilibrium Green's function technique, it is found that the TER ratio as high as ${10}^{7}%$ can be achieved. Analysis shows that it originates from the difference in the work functions of the contact surfaces of the two ferroelectric materials, which makes charge transfer occur or not occur between them and further leads to a metalinsulator switching of the ferroelectric vdW heterostructure upon the reversion of the applied…

Wannier functions are a powerful tool for the determination of topological properties of solids based on band structure calculations. Here, the authors present a simple and efficient scheme to obtain symmetry-conserving Wannier functions especially suitable for local orbital codes. They analyze which approximation of the basis contribution to the Berry connection and curvature matrices preserves symmetry and argue which Bloch function gauge is best suited for model systems, where the basis is not explicitly known.

Intrinsically gapless symmetry-protected topological phases (igSPT) are gapless systems with SPT edge states with properties that could not arise in a gapped system with the same symmetry and dimensionality. igSPT states arise from gapless systems in which an anomaly in the low-energy (infrared) symmetry group emerges from an extended anomaly-free microscopic (ultraviolet) symmetry. We construct a general framework for constructing lattice models for igSPT phases with emergent anomalies classified by group cohomology, and establish a direct connection between the emergent anomaly, group-extension, and topological edge states by gauging the extending symmetry. In many examples, the edge-state protection has a physically transparent mechanism: the extending UV symmetry operations pump lower-dimensional SPTs onto the igSPT edge, tuning the edge to a (multi)critical point between different SPTs protected by the IR symmetry. In two- and three-dimensional systems, an additional possibility is that the emergent anomaly can be satisfied by an anomalous symmetry-enriched topological order,…

The authors present a systematic and comprehensive theoretical study of Ga vacancy and interstitial migration in monoclinic gallium sesquioxide, based on hybrid functional calculations and the nudged elastic band technique. Notably, it is shown that the Ga vacancy can form a favorable three-split configuration, consisting of three Ga vacancies and two Ga interstitials, which enables migration with a dramatically lower migration barrier than previously calculated, further demonstrating the important role of split vacancies in this material.

A nonperturbative lattice regularization of chiral fermions and bosons with anomaly-free chiral symmetry $G$ in $1+1\mathrm{D}$ spacetime is proposed. More precisely, we ask ``whether there is a local short-range quantum Hamiltonian with a finite Hilbert space for a finite system realizing on-site symmetry $G$ defined on a 1D spatial lattice with continuous time, such that its low-energy physics produces a $1+1\mathrm{D}$ anomaly-free chiral matter theory of symmetry $G$?'' In particular, we propose that the chiral fermion theory with chiral U(1) ${3}_{L}\text{\ensuremath{-}}{5}_{R}\text{\ensuremath{-}}{4}_{L}\text{\ensuremath{-}}{0}_{R}$ symmetry, with two left-moving fermions of charge 3 and 4, and two right-moving fermions of charge 5 and 0 at IR low energy, can emerge from a 1D UV spatial lattice with a chiral U(1) symmetry, if we include properly designed multi-fermion interactions with intermediate strength (i.e., the dimensionless coupling constant is naturally order 1). In general, we propose that any $1+1\mathrm{D}$ U(1)-anomaly-free chiral matter theory can be defined as a…

Even in the absence of unitary evolution, measurements alone can induce a rich variety of dynamical phases and phenomena in many-body quantum systems. Inspired by the Kitaev honeycomb Hamiltonian, a paradigmatic model of topological physics, the authors construct here a stochastic measurement-only dynamics on a honeycomb lattice and show that it hosts distinct entanglement phases, including phases that protect topological qubits for an exponential amount of time and a critical phase with exotic dynamical scaling.

Establishing quantum spin liquid physics in microscopic models is a daunting task due to a variety of competing low-energy states, requiring sophisticated computational approaches to find the true ground state. Here, the authors present such a technique, based on neural networks with space-group symmetry, to obtain significantly improved ground-state wave functions of frustrated Heisenberg models. The authors also use this approach to find excited states and provide a blueprint for testing analytical predictions from spin-liquid theories.

Crystal structure, thermodynamic properties, and adiabatic demagnetization refrigeration (ADR) effect in the spin-$\frac{7}{2}$ triangular antiferromagnet $\mathrm{KBaGd}{({\mathrm{BO}}_{3})}_{2}$ are reported. With the average nearest-neighbor exchange coupling of 44 mK, this compound shows magnetic order below ${T}_{N}=263$ mK in zero field. The ADR tests reach the temperature of ${T}_{min}=122\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$, more than twice lower than ${T}_{N}$, along with the entropy storage capacity of 192 mJ ${\mathrm{K}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and the hold time of more than 8 h in the PPMS setup, both significantly improved compared to the spin-$\frac{1}{2}\phantom{\rule{4pt}{0ex}}{\mathrm{Yb}}^{3+}$ analog. We argue that $\mathrm{KBaGd}{({\mathrm{BO}}_{3})}_{2}$ shows a balanced interplay of exchange and dipolar couplings that together with structural randomness and geometrical frustration shift ${T}_{min}$ to well below the ordering temperature ${T}_{N}$, therefore facilitating the cooling.

Inspired by the advancements in large language models based on transformers, we introduce the transformer quantum state (TQS): a versatile machine learning model for quantum many-body problems. In sharp contrast to Hamiltonian/task specific models, TQS can generate the entire phase diagram, predict field strengths with experimental measurements, and transfer such a knowledge to new systems it has never been trained on before, all within a single model. With specific tasks, fine-tuning the TQS produces accurate results with small computational cost. Versatile by design, TQS can be easily adapted to new tasks, thereby pointing towards a general-purpose model for various challenging quantum problems.

Chiral metasurfaces, with appealing properties for studying light-matter interactions at the nanoscale, have emerged as a promising platform for the realization of chiral optical responses, thereby showing advantages in chirality-related applications. The conventional approaches primarily concentrate on circular dichroism and the high $Q$ factor of the chiral resonances, while little attention has been paid to the aspects of flexibility and controllability in the modulation of optical chirality, further inhibiting the implementation of tunable and multifunctional chiral metadevices. Here, we employ a planar chiral silicon metasurface governed by bound states in the continuum (BICs) to unravel steerable chiral optical responses. In particular, the BIC-based intrinsic and extrinsic planar chiralities can be precisely steered by breaking the in-plane symmetry and the illumination symmetry, respectively. Moreover, a hybrid $\mathrm{Si}\text{\ensuremath{-}}{\mathrm{VO}}_{2}$ metasurface, manifested by the chiral coupled-mode theory, showcases the feasibility of actively tuning the…

We use Majorana operators to study entanglement dynamics under random free fermion unitary evolution and projective measurements in one dimension. For certain choices of unitary evolution, namely, those which swap neighboring Majorana operators, and measurements of neighboring Majorana bilinears, one can map the evolution to the statistical model of completely packed loops with crossings (CPLC) and study the corresponding phase diagram. We generalize this model using the language of fermionic Gaussian states to a general free fermion unitary evolution acting on neighboring Majorana operators and numerically compute its phase diagram. We find that both the Goldstone and area-law phases persist in this new phase diagram, but with a shifted phase boundary. One important qualitative aspect of the new phase boundary is that even for the case of commuting measurements, the Goldstone phase persists up to a finite nonzero measurement rate. This is in contrast with the CPLC, in which noncommuting measurements are necessary for realizing the Goldstone phase. We also numerically compute the…

Magnetic excitations in layered magnetic materials that can be thinned down to the two-dimensional (2D) monolayer limit are of great interest from a fundamental point of view and for applications. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered $A$-type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response (i) through the variations of the scattered intensities, (ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and (iii) through the observation below the N\'eel temperature $({T}_{N})$ of second-order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently…

Using the method developed in the companion paper [O. Vafek and J. Kang, Continuum effective Hamiltonian for graphene bilayers for an arbitrary smooth lattice deformation from microscopic theories, Phys. Rev. B 107, 075123 (2023)], we construct effective continuum theories for two different microscopic tight-binding models of twisted bilayer graphene at a twist angle of $1.{05}^{\ensuremath{\circ}}$, one Slater-Koster based and the other ab initio Wannier based. The energy spectra obtained from the continuum theory---either for rigid twist or including lattice relaxation---are found to be in nearly perfect agreement with the spectra from tight-binding models when the gradient expansion is carried out to second order, demonstrating the validity of the method. We also analyze the properties of the Bloch states of the resulting narrow bands, finding non-negligible particle-hole symmetry breaking near the $\mathrm{\ensuremath{\Gamma}}$ point in our continuum theory constructed for the ab initio-based microscopic model due to a term in the continuum theory that was previously overlooked.…

Manipulation of the valley degree of freedom provides a paradigm in quantum information technology. Here, through first-principles calculations and model analysis, we demonstrate that monolayer ${\mathrm{Cr}}_{2}\mathrm{COOH}$ MXene is a promising candidate material for valleytronics applications. We reveal that ${\mathrm{Cr}}_{2}\mathrm{COOH}$ is a ferromagnetic semiconductor and harbors valley features. Due to the simultaneous breaking inversion symmetry and time-reversal symmetry, the valleys are polarized spontaneously. Moreover, the valley polarization is sizable in both the valence and conduction bands, benefiting the observation of the anomalous valley Hall effect. More remarkably, the valley splitting can be effectively tuned by the magnetization direction, strain, and ferroelectric substrate. More interestingly, the ferroelectric substrate ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$ can not only regulate the MAE, but also tune valley polarization state. Our findings offer a practical way for realizing highly tunable valleys by multiferroic couplings.

We show that a local non-Hermitian perturbation in a Hermitian lattice system generically induces scale-free localization for the continuous-spectrum eigenstates. When the perturbation lies at a finite distance to the boundary, the scale-free eigenstates are promoted to exponentially localized modes, whose number is proportional to the distance. Furthermore, when the local non-Hermitian perturbation respects parity-time $(\mathcal{PT})$ symmetry, the $\mathcal{PT}$ symmetry breaking is always accompanied by the emergence of scale-free or exponential localization. Intriguingly, we find a concise band-structure condition which tells not only when the continuous-spectrum $\mathcal{PT}$ breaking of scale-free modes can occur but also the precise $\mathcal{PT}$-breaking energy window. Our results uncover a series of unexpected generic phenomena induced by a local non-Hermitian perturbation, which has interesting interplay with $\mathcal{PT}$ symmetry.

We introduce an efficient method to simulate the dynamics of an interacting quantum impurity coupled to noninteracting fermionic reservoirs. Viewing the impurity as an open quantum system, we describe the reservoirs by their Feynman-Vernon influence functionals (IFs). The IFs are represented as matrix-product states in the temporal domain, which enables an efficient computation of the dynamics for arbitrary interactions. We apply our method to study quantum quenches and transport in an Anderson impurity model, including highly nonequilibrium setups, and find a favorable performance compared to state-of-the-art methods. The computational resources required for an accurate computation of the dynamics scale polynomially with evolution time, indicating that a broad class of out-of-equilibrium quantum impurity problems are efficiently solvable. This approach will provide additional insights into the dynamical properties of mesoscopic devices and correlated materials.

We demonstrate the potential of van der Waals magnets for spintronic applications by reporting long-distance magnon spin transport in the electrically insulating antiferromagnet chromium thiophosphate ($\mathrm{Cr}\mathrm{P}{\mathrm{S}}_{4}$) with perpendicular magnetic anisotropy. We inject and detect magnon spins nonlocally by Pt contacts and monitor the nonlocal resistance as a function of an in-plane magnetic field up to 7 T. We observe a nonlocal resistance over distances up to at least a micron below the N\'eel temperature (${T}_{\mathrm{N}}=38$ K) close to magnetic field strengths that saturate the sublattice magnetizations.

Charge transport plays a crucial role in manifold potential applications of two-dimensional materials, including field-effect transistors, solar cells, and transparent conductors. At most operating temperatures, charge transport is hindered by scattering of carriers by lattice vibrations. Assessing the intrinsic phonon-limited carrier mobility is thus of paramount importance to identify promising candidates for next-generation devices. Here we provide a framework to efficiently compute the drift and Hall carrier mobility of two-dimensional materials through the Boltzmann transport equation by relying on a Fourier-Wannier interpolation. Building on a recent formulation of long-range contributions to dynamical matrices and phonon dispersions [Phys. Rev. X 11, 041027 (2021)], we extend the approach to electron-phonon coupling including the effect of dynamical dipoles and quadrupoles. We identify an unprecedented contribution associated with the Berry connection that is crucial to preserve the Wannier-gauge covariance of the theory. This contribution is not specific to two-dimensional…

We propose an ab initio Boltzmann transport approach taking into account magnon-phonon scattering (MPS) and three-phonon scattering simultaneously to accurately evaluate the thermal transport properties of ferromagnetic crystals. Using this approach, we studied the nonelectronic thermal transport properties of the body-centered cubic iron as a case. The reasonable agreement between our calculation results and the available experimental data suggests that phonons dominate the nonelectronic thermal conduction at high temperatures, and magnons may contribute to the thermal conductivity only at low temperatures. Remarkably, the abnormal increase in the magnon thermal conductivity at high temperatures implies that other magnon-involved scattering events instead of MPS should dominate the magnon thermal conductivity. Moreover, analyses of average scattering rates and heat propagation lengths suggest that hydrodynamic heat transport may occur at low temperatures. This new approach fills the gap in the first-principles evaluation of the coupled magnon-phonon thermal transport properties in…

Proximity effects in van der Waals heterostructures offer controllable ways to tailor the electronic band structure of adjacent 2D materials. Here, the authors perform extensive first-principles calculations, to reveal the impact of twisting, gating, stacking, interlayer distance, and encapsulation, on the spin-orbit proximitized Dirac bands in graphene/transition metal dichalcogenide heterostructures. Furthermore, the authors make specific predictions for experimentally measurable quantities, such as charge-to-spin conversion efficiency. The results highlight the enormous tunability potential of proximity-induced phenomena in van der Waals heterostructures.

Although condensed matter systems usually do not have higher-form symmetries, we show that, unlike 0-form symmetry, higher-form symmetries can emerge as exact symmetries at low energies and long distances. In particular, emergent higher-form symmetries at zero temperature are robust to arbitrary local UV perturbations in the thermodynamic limit. This result is true for both invertible and noninvertible higher-form symmetries. Therefore emergent higher-form symmetries are exact emergent symmetries: they are not UV symmetries but constrain low-energy dynamics as if they were. Since phases of matter are defined in the thermodynamic limit, this implies that a UV theory without higher-form symmetries can have phases characterized by exact emergent higher-form symmetries. We demonstrate this in three lattice models, the quantum clock model and emergent ${\mathbb{Z}}_{N}$ and $\mathrm{U}(1)\phantom{\rule{4pt}{0ex}}p$-gauge theory, finding regions of parameter space with exact emergent (anomalous) higher-form symmetries. Furthermore, we perform a generalized Landau analysis of a…

Quantum systems subject to external monitoring manifest a rich phenomenology in their entanglement properties. Here, the authors use quantum Fisher information to uncover a multipartite entanglement phase transition in the monitored quantum Ising chain. By changing the measurement rate, they observe a shift from bounded to long-range multipartiteness of quantum correlations. They show that the quantum Fisher information displays distinct behavior from the entanglement entropy, and the two outline different phase boundaries.

What drives superconductivity in non-moir\'e graphene? Here, an electron-electron mechanism is applied to the continuum framework of Bernal bilayer and rhombohedral trilayer graphene. Within a Kohn-Luttinger-like approach, the internal screening of the long-range Coulomb potential leads to an effective attraction between carriers, enabling the formation of Cooper pairs. The calculations provide a filling-dependent critical temperature that is remarkably enhanced due to Ising spin-orbit coupling, and determine the spin-triplet valley-singlet symmetry of the superconducting order parameter, in line with recent experimental advances.

We investigate the strong coupling between excitons and quasibound states in the continuum (BICs) resonance in a bulk ${\mathrm{WS}}_{2}$ metasurface. Here, we employ bulk ${\mathrm{WS}}_{2}$ to construct an ultrathin nanodisk metasurface, supporting the symmetry-protected magnetic dipole quasi-BIC resonance, which can self-hybridize with the excitons and lead to a strong light-matter interaction enhancement within the structure without the necessity for an external cavity. This strong coupling can be characterized by the considerable Rabi splitting of 159 meV and the clearly anticrossing behavior appearing in the absorption spectrum. Furthermore, we analyze such light-matter coupling by constructing a Hamiltonian model including the surplus excitons and tune the interaction from weak- to strong-coupling regimes via the tunability radiation loss of the quasi-BIC resonance. Our results have great potential for manipulating the exciton-polaritons at room temperature and provide a promising prospect for photonic devices that exploit strong coupling in applications.

Amorphous silica (a-${\mathrm{SiO}}_{2}$) is a foundational disordered material for which the thermal transport properties are important for various applications. To accurately model the interatomic interactions in classical molecular dynamics (MD) simulations of thermal transport in a-${\mathrm{SiO}}_{2}$, we herein develop an accurate yet highly efficient machine-learned potential model that allows us to generate a-${\mathrm{SiO}}_{2}$ samples closely resembling experimentally produced ones. Using the homogeneous nonequilibrium MD method and a proper quantum-statistical correction to the classical MD results, quantitative agreement with experiments is achieved for the thermal conductivities of bulk and 190-nm-thick a-${\mathrm{SiO}}_{2}$ films over a wide range of temperatures. To interrogate the thermal vibrations at different temperatures, we calculated the current correlation functions corresponding to the transverse acoustic and longitudinal acoustic collective vibrations. The results reveal that, below the Ioffe-Regel crossover frequency, phonons as well-defined excitations…

The authors study the quantum dynamics of a (2+1)D monitored random circuit involving local projective measurements, inspired by the physics of the Kitaev quantum spin liquid. A Majorana parton description of the dynamics reveals a close connection between the entanglement dynamics of quantum trajectories and the 3D classical fully packed loop model. The authors uncover a critical phase where quantum trajectories exhibit long-range entanglement with a logarithmic ($L$ log $L$) violation of the area law, and a topologically ordered phase reminiscent of the toric code phase.

Enhanced circular dichroism (CD) signal is crucial for ultrasensitive detection of chiral species. This purpose strongly relies on the construction of superchiral field in achiral resonant nanostructures. Despite the progress, the research on superchiral fields and their related physics is fundamentally restricted. Here, we demonstrate an approach to construct superchiral field in achiral metasurfaces and explore its impact on chiral mode interaction. While the chiral field at individual bound states in the continuum (BIC) is small, all criteria for giant superchiral fields can be satisfied when two BICs with orthogonal polarizations are merged. Consequently, the typical photonic crystal slabs can produce superchiral fields with enhancement factors ($C\text{/}{C}_{\mathrm{CPL}}$) (where CPL is circular polarized light) orders of magnitude higher than state of the art in nanostructures. More interestingly, a type of chiral light-matter interaction has been revealed by introducing chiral active materials. The nearly orthogonal BICs couple one another at the merging point and result in…

Recent experiments on $t$MoTe${}_{2}$ provide the first realization of the fractional quantum anomalous Hall effect. Synthesizing insights from an extensive exact diagonalization study, the authors present here a many-body phase diagram $t$MoTe${}_{2}$, in which lowest Landau level (LLL)-like features and non-LLL-like features coexist. The study highlights several guiding principles, including interaction-enhanced particle-hole asymmetry, that is expected to play an important role in general fractional quantum anomalous Hall systems.

We study many-body localization (MBL) transition in disordered Floquet systems using a polynomially filtered exact diagonalization (POLFED) algorithm. We focus on disordered kicked Ising model and quantitatively demonstrate that finite-size effects at the MBL transition are less severe than in the random field XXZ spin chains widely studied in the context of MBL. Our conclusions extend also to other disordered Floquet models, indicating smaller finite-size effects than those observed in the usually considered disordered autonomous spin chains. We observe consistent signatures of the transition to MBL phase for several indicators of ergodicity breaking in the kicked Ising model. Moreover, we show that an assumption of a power-law divergence of the correlation length at the MBL transition yields a critical exponent $\ensuremath{\nu}\ensuremath{\approx}2$, consistent with the Harris criterion for one-dimensional disordered systems.

In this work, we present and analyze two tensor network-based influence functional approaches for simulating the real-time dynamics of quantum impurity models such as the Anderson model. Via comparison with recent numerically exact simulations, we show that such methods accurately capture the long-time nonequilibrium quench dynamics. The two parameters that must be controlled in these tensor network influence functional approaches are a time discretization (Trotter) error and a bond dimension (tensor network truncation) error. We show that the actual numerical uncertainties are controlled by an intricate interplay of these two approximations, which we demonstrate in different regimes. Our work opens the door to using these tensor network influence functional methods as general impurity solvers.

Janus structures with the breaking of out-of-plane mirror symmetry have gained intensive attention. Here, on the basis of first principles, we not only investigate the recently discovered Janus 2H-MoSH monolayer [ACS Nano 15, 20319 (2021)], but also report the global minimum structure of a Janus 1T-MoSH monolayer. Meanwhile, 2H-MoSH monolayer can easily transform into the 1T phase, overcoming a relatively small barrier of 0.13 eV. Intriguingly, Janus 1T-MoSH is a charge-density wave (CDW) material and its CDW order can be regulated via external strains. When Janus 1T-MoSH is subjected to 3% compressive strain, its CDW is completely suppressed and a superconducting state with a superconducting transition temperature $\mathit{T}{}_{c}$ of 25.15 K emerges. Moreover, Janus 2H-MoSH monolayer is an intrinsic superconductor with a $\mathit{T}{}_{c}$ of $\ensuremath{\sim}26.81$ K and its $\mathit{T}{}_{c}$ can be enhanced up to 36.69 K under a 1% tensile strain. Our work provides more in-depth insights for superconducting and CDW in low-dimensional transition metal dichalcogenides and…

In bulk superconductors or Josephson junctions formed in materials with spin-orbit interaction, the critical current can depend on the direction of current flow or of applied magnetic field, an effect known as the superconducting (SC) diode effect. Here, we consider the SC diode effect in Josephson junctions in nanowire devices. We find that the $4\ensuremath{\pi}$-periodic contribution of Majorana bound states (MBSs) to the current phase relation (CPR) of single junctions results in a significant enhancement of the SC diode effect when the device enters the topological phase and can therefore be used as an indicator of the phase transition. Crucially, this enhancement of the SC diode effect is independent of the parity of the junction and therefore protected from parity-altering events, such as quasiparticle poisoning, which have hampered efforts to directly observe the $4\ensuremath{\pi}$-periodic CPR of MBSs. We show that this effect can be generalized to SQUIDs and that, in such devices, the parity-protected SC diode effect can provide a highly controllable probe of the topology…

The recently synthesized ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ monolayer [Science 369, 670 (2020)] exhibit outstanding environmental stability, moderate band gap, and excellent mechanical properties, which opens up a new avenue for the explorations of two-dimensional (2D) ${\mathrm{MA}}_{2}{\mathrm{Z}}_{4}$ materials. Inspired by this finding, we perform comprehensive structural predictions of ${\mathrm{MSi}}_{2}{\mathrm{N}}_{4}$ monolayers with lanthanide and actinide metals at the M site. Using the CALYPSO structural search method and first-principles calculations, we identify seven ${\mathrm{MSi}}_{2}{\mathrm{N}}_{4}$ monolayers with robust ambient stabilities, four of which are metals (M = Tm, Lu, Pa, Np) and three are semiconductors (M = Ce, Th, U). Of particular interest is the ${\mathrm{ThSi}}_{2}{\mathrm{N}}_{4}$ monolayer, which is an indirect-gap semiconductor with ultra-high electron mobility of 14384 ${\mathrm{cm}}^{2}\phantom{\rule{0.28em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.28em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Our results enrich the 2D…

Useful in the enhancement of light-matter interaction, localization of light is at the heart of photonics studies. Different approaches have been proposed to localize light, including those based on dynamical localization, topological trivial or nontrivial defects in the band gap of photonic crystals, and bound states in the continuum. Recent studies on the non-Hermitian skin effect have provided us new means to localize waves. Inspired by two recent studies [Li et al., Phys. Rev. Lett. 128, 223903 (2022); Zhu and Gong, Phys. Rev. B 106, 035425 (2022)], we propose an innovative method towards localized light in continuous systems via photonic corner skin modes, which are hybrid skin-topological modes as a special kind of second-order non-Hermitian skin effect with symmetrically distributed gain and loss. Specifically, we propose to make use of weak pseudoinversion symmetric gain and loss, which does not close the band gap of the system, to realize a non-Hermitian photonic Chern insulator with chiral edge states. The chiral edge states then accumulate at certain corners of the…

Intense scrutiny over the last decade of experiments on a variety of platforms aiming to identify topological superconductivity has raised the stakes in this search. Because nontopological Andreev bound states at or near zero energy can resemble topological states, signatures beyond spectroscopy of zero-energy modes are called for. A key signature of a topological phase transition - namely, the closing and reopening of the superconducting gap - is mostly unobserved in previous experiments. Here, this phenomenon is reported in planar Josephson junction devices made from superconductor-semiconductor hybrid materials. Consistency between experiment and numerics, along with a number of other characteristic signatures, including dependence on phase, magnetic field, and chemical potential, support the conclusion that the observed gap closing and reopening, with associated appearance of a zero-bias conductance peaks upon reopening, are associated with topological transition.

The authors introduce here WAPNET, a periodic neural network (NN) variational ansatz for solving the ground state of a homogeneous electron gas with high accuracy over a broad range of the density coupling constant ${r}_{s}$. Going beyond recent work for molecules, this contribution establishes NN models as flexible and powerful ansatz for electronic structure calculations in extended systems. In all density regimes, WAPNET-based variational Monte Carlo results are comparable to or better than state-of-the-art benchmarks obtained by diffusion Monte Carlo with iterative backflow.

The non-Bloch band theory can describe energy bands in a one-dimensional (1D) non-Hermitian system. On the other hand, whether the non-Bloch band theory can be extended to higher-dimensional non-Hermitian systems is nontrivial. In this work, we construct the non-Bloch band theory in two classes of two-dimensional non-Hermitian systems by reducing the problem to that for a 1D non-Hermitian model. In these classes of systems, we get the generalized Brillouin zone for a complex wave vector and investigate topological properties. In the model of the non-Hermitian Chern insulator, as an example, we show the bulk-edge correspondence between the Chern number defined from the generalized Brillouin zone and the appearance of the edge states.