The interplay of strong atomic spin-orbit coupling with Jahn-Teller (JT) lattice distortions is an important theme in quantum materials hosting heavy atoms. A prototypical example of such a system is a degenerate $j=3/2$ multiplet coupled to local phonon modes. Here, we study the multipolar ground states of this system as realized in Mott insulators, explore its thermal phase diagram via an $SU\left(4\right)$ spin Monte Carlo approach coupled to JT phonons, and study the resulting temperature dependent spectral distribution of the $j=3/2$ multiplet. Our work sheds light on coexisting distinct multipolar orders engendered by phonon coupling, role of thermal JT fluctuations, and the entropy of the coupled multipole-phonon system. We discuss broad implications for double perovskites ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6, {\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$ and lacunar spinels such as ${\mathrm{GaTa}}_4{\mathrm{Se}}_8$ and ${\mathrm{GaNb}}_4{\mathrm{Se}}_8$.

This study resolves a previously reported mechanical instability of the experimentally observed superconducting P4/ncc phase of ${\mathrm{Mg}}_4{\mathrm{AlSi}}_3$ using first-principles calculations. Previous theoretical work reported a negative ${\mathrm{C}}_{66}$ elastic constant for the P4/ncc structure and consequently proposed a lower symmetry Pccn structure as the mechanically stable phase. Here, we reinvestigate the elastic properties of P4/ncc ${\mathrm{Mg}}_4{\mathrm{AlSi}}_3$ using both energy-strain and stress-strain approaches. We find that all independent elastic constants are positive and satisfy the mechanical stability criteria, with the two approaches yielding consistent results. The absence of imaginary modes in the calculated phonon dispersion further establishes the dynamical stability of the phase, with the negative formation enthalpy indicating its thermodynamic stability. We further investigate for the first time the microscopic origin of its superconductivity through the electron-phonon coupling calculations based on Migdal-Eliashberg theory. The calculated electron-phonon coupling constant $\lambda$ of 0.618 and a logarithmic average frequency of 205.174 K, lead to a superconducting transition temperature $T_c$ of 5.123 K, in close agreement with the experimental value of 5.2 K. Therefore our results resolve the previous discrepancy concerning the mechanical stability of the experimentally realized P4/ncc phase and provide a consistent microscopic description of its lattice stability and phonon-mediated superconductivity.

We investigate how long-range power-law interactions ($V\propto r^{-\alpha }$) influence the finite-size stability of many-body localization against boundary-induced thermalization in a one-dimensional disordered Heisenberg spin chain. Whereas previous studies have primarily examined avalanche instabilities through perturbative analyses or short-range models, we adopt an open-system approach that directly probes the dynamical response of a localizedlike regime to a controlled boundary thermalizing perturbation. By combining exact diagonalization of static properties with Lindblad master-equation simulations, we systematically examine the interplay among the interaction exponent $\alpha$, disorder strength $W$, and system size $L$. A finite-size scaling analysis of the half-chain entanglement entropy identifies an effective crossover near $\alpha \simeq 2$, separating a strongly long-range regime exhibiting enhanced delocalizing tendencies from a short-range-like regime with more robust localization signatures. To characterize avalanchelike dynamics, we couple one boundary of the chain to an infinite-temperature bath that serves as a minimal thermalizing seed and monitor the resulting bath-induced decay of the staggered magnetization imbalance. Within the accessible system sizes and simulation times, the characteristic threshold time is well described by the empirical scaling relation $T_{r_{\mathrm{th}}}\sim exp\left[\kappa \left(\alpha \right)LW\right]$, where the coefficient $\kappa \left(\alpha \right)$ increases monotonically with increasing interaction exponent. This trend demonstrates that shorter-range interactions provide substantially stronger resistance to boundary-induced thermalization in the strongly disordered regime. Motivated by this scaling behavior, we introduce an interaction-dependent disorder scale $W_{\mathrm{stab}}\left(\alpha \right)$ as an operational measure of avalanche resistance. Rather than representing a sharp thermodynamic phase boundary, this quantity provides a conservative, protocol-dependent characterization of finite-size dynamical stability. Our results show that long-range interactions facilitate bath-induced thermalization, whereas increasing the interaction exponent significantly enhances the robustness of localizedlike behavior against boundary perturbations.

The magnetoelectric (ME) effect, the induction of electric polarization ($P$) by an applied magnetic field or magnetization ($M$) by an electric field, provides a pathway for low-power-consumption data memory devices. In this work, we present a systematic experimental investigation of the magnetism, heat capacity, and anisotropic ME effect in $\mathrm{BaN}{\mathrm{i}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_2$ single crystals. Our results reveal long-range antiferromagnetic (AFM) ordering below the Néel temperature $T_N=24\mathrm{K}$, where the $\mathrm{N}{\mathrm{i}}^{2+}$ spins are AFM aligned along the $x$ // [1-10] axis. Detailed ME measurements reveal that $\mathrm{BaN}{\mathrm{i}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_2$ exhibits dominant out-of-plane electric polarization and significant in-plane electric polarization along the $y$ // [110] direction. The largest magnetically induced electric polarization of 128 $\mu \mathrm{C}/{\mathrm{m}}^2$ along the $z$ // [001] axis is observed at $T =2$ K under the magnetic field of ${\mu }_{0}H=9$ T applied along the $x$ direction, with a ME coefficient of α $\sim 16.8$ ps/m. The angular-dependent measurement demonstrates that the induced in-plane electric polarization $P_y$ changes its direction by −2θ around the $z$ axis upon rotating the magnetic field $H$ by an angle θ. Based on the crystal and magnetic symmetry of the honeycomb layer, the microscopic origin of in-plane electric polarization $P_x$ and $P_y$ under $H$ // $z$ and $P_y$ under $H$ // $x$ and $H$ // $y$ can be attributed to the inverse Dzyaloshinskii-Moriya mechanism and the spin-dependent $p\text{−}d$ hybridization mechanism, respectively. Thus, in this work, we provide insights for understanding the microscopic origin of the ME coupling in linear ME materials.

Infrared singularities of gapless Goldstone modes preclude magnetic long-range order at finite temperature in conventional two-dimensional systems. By studying the spin-$S$ Heisenberg model on regular tilings of the hyperbolic plane, we show that this obstruction is absent in negatively curved space. Using spin-wave theory, we find that the zero-energy collective modes required by symmetry carry vanishing local spectral weight and are separated from the thermodynamic bulk magnon continuum by a finite gap in the bulk local spectral density. As a result, local transverse correlations remain short-ranged, with a finite correlation length, despite the presence of Goldstone modes associated with the broken $\mathrm{SO}\left(3\right)$ spin-rotation symmetry. Stronger negative curvature is found to suppress quantum fluctuations in bulk thermodynamic quantities, pushing the ordered state toward “mean-field-like” behavior. We further estimate the ordering temperature from the thermal spin-wave correction to the ordered moment. These results establish hyperbolic geometry as a route to finite-temperature magnetic order that circumvents the Mermin-Wagner obstruction without breaking or modifying the continuous symmetry.

We develop a general framework based on the sign patterns of Lyapunov exponents for engineering and characterizing counterintuitive localization properties in one-dimensional non-Hermitian quasiperiodic lattices. On the one hand, for the Anderson localized states in the bulk under the periodic boundary condition, we find that their localization features can be boundary sensitive, becoming boundary-localized skin modes under the open boundary condition. On the other hand, for nonlocalized states, the well-known extended-localized duality relation can break down, as their counterparts in the dual model can also be nonlocal. We discuss how these remarkable phenomena can be understood from the perspective of Lyapunov exponents, highlighting the interplay of non-Hermiticiy and quasiperiodicity.

van der Waals antiferromagnets provide a route to thickness-controlled magnetic order, but few combine high-temperature Ising order with conducting, correlated, and topological electronic structure. Here we show that UOTe realizes this combination. Magnetic susceptibility reveals a strongly anisotropic paramagnetic response, while neutron diffraction establishes $c$-axis antiferromagnetic order below $T_{\mathrm{N}}\approx 150\mathrm{K}$ with an order-parameter exponent $\beta =0.14$, close to the two-dimensional Ising value. Torque magnetometry further shows that the ordered state remains well described by a uniaxial antiferromagnet below the high-field metamagnetic transition. Pulsed-field magnetization up to $73\mathrm{T}$ shows that the ordered state survives to very large fields applied along the $c$ axis before entering a broad metamagnetic regime that begins near $50\mathrm{T}$ and remains unsaturated at the highest measured field. Angle-dependent proximity detector oscillator measurements show that the metamagnetic instability is set by the field component along the ordered moment direction, providing direct evidence for Ising-like field rigidity. UOTe therefore establishes a field-rigid Ising antiferromagnet with giant metamagnetic transition fields in a compensated van der Waals metal, where high-temperature $c$-axis order, quasi-two-dimensional magnetic criticality, Kondo-associated uranium $5f$ hybridization, metallic transport, and symmetry-enabled topology coexist in a single material.

Body-centered-cubic $\mathrm{Ca}{\mathrm{H}}_6$ has attracted considerable attention due to its unique hydrogen clathrate structure and high-$T_{\mathrm{c}}$ superconductivity ($T_{\mathrm{c}}=215\mathrm{K}$ at 172 GPa). Although hydrogen vacancy in this hydride has been reported experimentally, its effects on structural and superconducting properties remain unclear. By comparing with the experimental equation of state, our path-integral molecular dynamics simulations reveal that pressure reduction induces hydrogen depletion from interstitial sites of the Ca sublattice, resulting in the formation of a nonstoichiometric $\mathrm{Ca}{\mathrm{H}}_{6-\delta }$ phase $\left(\delta \le 0.45\right)$ below 165 GPa. The increase in hydrogen vacancies induces thermoelastic instability below 125 GPa (at 300 K) through shear-modulus softening, while concurrently suppressing superconductivity via electronic-state modulation, with the $T_{\mathrm{c}}$ decreasing at a rate of $2.3\mathrm{K}/\mathrm{GPa}$. Both results align with experimental observations. Moreover, we predict that hydrogen vacancies facilitate hydrogen diffusion in the superconducting $\mathrm{Ca}{\mathrm{H}}_{6-\delta }$ phase between 145 and 160 GPa, with the diffusivity reaching or exceeding ${10}^{-8}\mathrm{c}{\mathrm{m}}^2/\mathrm{s}$. The findings emphasize the key role of hydrogen vacancy in understanding the high-pressure evolution behavior of high-$T_{\mathrm{c}}$ hydrides.

Discrete time crystals (DTCs) have emerged as a novel nonequilibrium phenomenon, exhibiting spontaneous symmetry breaking of discrete time translation symmetry, and holding promise for applications ranging from enhancing quantum sensing to protecting quantum entanglement. Nevertheless, analytical quantification for disordered DTCs remains challenging, leaving uncertainties about their behaviors in large scale systems amid current debates on the stability of (Floquet-)many-body localization. In this work, we introduce an analytical framework to calculate the values of key observables in a strongly disordered DTC without fitting parameter. The perturbatively obtained closed-form formulas show quantitative agreement with numerical simulations for inverse participation ratios for eigenstate localization in Fock space, Edwards-Anderson parameters for spin-glass orders, mutual information for long-range entanglement, and the steady-state amplitudes of autocorrelators for period-doubled oscillations. Meanwhile, we demonstrate that eigenstate resonances render the scaling for the deviation of physical observables from their unperturbed values as $O\left(\lambda \right)$, in contrast to nonresonant situations with suppressed deviation $O\left({\lambda }^2\right)$. Our newly developed scheme adopts resolvent perturbation formalism, which can directly prescribe arbitrarily higher-order corrections without iterations. With such advantages, we analytically prove that quasienergy corrections for pairwise cat eigenstates are identical up to order $O\left({\lambda }^{(L/n_{\text{op}})-1}\right)$, where perturbations of strength $\lambda$ involve at most $n_{\text{op}}$-spin terms. Such spectral pairing deviations quantify the DTC lifetime as ${\tau }_{*}\sim {(1/\lambda )}^{L/n_{\text{op}}}$. We further show that the analytical framework applies to generic DTC models with dominant Ising interaction and a given number of qubits, offering a unified scheme to quantify physical observables for systems beyond numerically accessible sizes, with or without disorders.

Two-dimensional (2D) altermagnets (AMs), characterized by distinctive spin splitting and robustness against external fields, have emerged as promising candidates for spintronic device applications. Exploring multipiezo effects in 2D AMs through precise and energy-efficient modulation strategies has become crucial for realizing their multifunctional applications. In this work, we demonstrate that the $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer is a 2D AM with a pronounced spin splitting of 0.45 eV for valence bands. The $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer exhibits valley degeneracy at the ${\mathrm{X}/\mathrm{X}}^{\prime }$ valleys, which is protected by $\left[C_2\parallel C_{4z}\right]$ and $\left[C_2\parallel M_{xy}\right]$ symmetries. Uniaxial strain as an energy-efficient modulation strategy breaks the balance of these symmetries. This imbalance induces piezomagnetic and piezovalley effects in $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer, accompanied by the emergence of an anomalous valley Hall effect. Furthermore, $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer possesses a Janus structure, which enables significant in-plane and out-of-plane piezoelectric effects under uniaxial strain. The multipiezo effects make the Janus $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer a promising platform for the development of multifunctional spintronic devices.

Topological phases in metamaterials are often inferred from localized edge states or from real-space wave-function measurements. Yet the topology is fundamentally encoded in the bulk eigenvectors and often manifests as a bulk band inversion. Here we directly access this band inversion in an exciton-polariton Su-Schrieffer-Heeger (SSH) chain using far-field spectroscopy with tuneable sublattice interference. The SSH chain provides an excellent benchmark model for establishing this measurement principle in an exciton-polariton platform. We show that in the SSH model, the band inversion is characterized by a sign change of the sublattice symmetry $\langle {\sigma }_{\mathrm{x}}\rangle$ between the Brillouin-zone center and boundary. A transverse sublattice displacement maps the relative phase between sublattice wave functions onto a controllable far-field interference phase $\mathrm{\Delta }\theta$. Taking the difference of spectra at $\mathrm{\Delta }\theta =0$ and $\mathrm{\Delta }\theta =\pi$ yields a quantity proportional to $\langle {\sigma }_{\mathrm{x}}\rangle$, directly revealing the band inversion in the topological configuration. The tunable phase $\mathrm{\Delta }\theta$ further lets us reconstruct the effective $2\times 2$ Bloch Hamiltonian and its winding number, unequivocally linking the measured band inversion to the topological invariant. More generally, spectroscopy with a controllable sublattice phase allows for the measurement of bulk eigenvectors, granting access to band inversions for higher-dimensional systems.

We present a detailed study of the real-time dynamics and spectral properties of the one-dimensional fermionic Hubbard model at infinite temperature. Using tensor network simulations in Liouville space, we compute the single-particle Green's function and analyze its dynamics across a broad range of interaction strengths. To complement the time-domain approach, we develop a high-resolution Chebyshev expansion method within the density matrix formalism, enabling direct access to spectral functions in the frequency domain. As interactions are introduced, a transition in the spectral function from a sharp, free-particle dispersion to a broadened two-band structure associated with hole and electron excitations is observed, and electron propagators are found to display a diffusive falloff. At infinite interaction strength ($U=\infty$), we exploit a determinant representation of the Green's function to access both real-time and spectral properties. In this regime, spectral functions retain a blurred, cosinelike momentum dispersion in frequency space indicating almost coherent propagation, while the dynamics display nontrivial light-cone spreading with an anomalous exponent $\alpha \approx 0.78$. Our results demonstrate that strong correlations and nontrivial quantum coherence can persist even at infinite temperature and infinite interaction strength.

The hybrid skin-topological effect (HSTE) arises from the interplay between the non-Hermitian skin effect and topologically protected edge states. Here, we investigate the HSTE associated with antichiral edge states. As a minimal model, we study a modified Haldane nanoribbon in which gain and loss are applied exclusively at the zigzag edges. We show that in antichiral systems, the HSTE originates from the interplay between edge modes and counterpropagating bulk modes, a mechanism distinct from that in conventional chiral systems. Remarkably, in sufficiently narrow ribbons, applying gain or loss to only one edge can induce a skin effect in states localized at the opposite edge. We refer to this phenomenon as a nonlocal antichiral skin effect. We further show that, in narrow systems, edge-localized dissipation can induce bulk skin modes when parity-time ($\mathcal{PT}$) symmetry is broken, while the bulk non-Hermitian skin effect is forbidden in the $\mathcal{PT}$-symmetric regime. These results imply that edge-localized gain and loss can control both the emergence and the localization direction of the bulk skin modes. Our findings establish a symmetry-based mechanism for controlling non-Hermitian skin effects via edge dissipation in antichiral systems.

We study the robustness of the Floquet quantum Ising model against integrability-breaking perturbations, focusing on the phase hosting both Majorana zero and $\pi$ modes. A recent work [H.-C. Yeh, A. Rosch, and A. Mitra, Phys. Rev. B 110, 075117 (2024)] observed that the Floquet product mode, a composite edge mode constructed from both Majorana operators, is considerably more robust than the individual Majorana edge modes. We analyze these strong modes from the point of view of the eigenphase order present in finite chains with open boundary conditions. As a result of the Majorana modes, all Floquet eigenstates come in quadruplets in the integrable limit. We show that the robustness of the various modes as well as the behavior of the boundary spin correlation functions can be understood in terms of the spectral statistics of these quadruplets in the presence of integrability-breaking perturbations.

The electronic, magnetic, valley, and magneto-optical properties of an intrinsic MnBi monolayer in the hexagonal phase are investigated using first-principles calculations including on-site Coulomb interactions and spin-orbit coupling. The monolayer exhibits a ferromagnetic ground state with pronounced magnetic anisotropy, which significantly modifies the low-energy electronic structure and induces magnetization-direction-dependent band gap openings. The Berry curvature and anomalous Hall conductivity are highly sensitive to the orientation of the magnetization. A sizable valley splitting emerges for out-of-plane magnetization, while it is nearly quenched for in-plane alignment, demonstrating a strong coupling between magnetic anisotropy and valley physics. Furthermore, charge doping, external electric fields, and mechanical strain provide efficient routes to tune the magnetization orientation and Curie temperature while preserving magnetic order. These results highlight the MnBi monolayer as a promising platform for two-dimensional spintronics, valleytronics, and magneto-optical applications.

We study the effects of cavity-mediated interactions on the symmetries and topological properties of a Su-Schrieffer-Heeger chain coupled to a single-mode photonic cavity. Considering an off-resonant regime we use the high-frequency expansion in order to obtain an effective fermionic Hamiltonian with cavity-mediated interactions. We characterize the effects of the cavity on topology in a finite-size chain by studying three different fermionic many-body topological markers using exact diagonalization: correlation functions between edges in a chain with open boundary conditions, and a winding number based on the single-particle Green's function and bulk electric polarization via the many-body formula by Resta for a chain with periodic boundary conditions. Importantly, we show that chiral symmetry is not broken by the cavity in the many-body ground state in the high-frequency limit. Our work highlights the importance of the cavity-mediated many-body interactions in understanding the symmetry and topology of the system.

We investigate bias-driven nonequilibrium quantum phase transitions in a paradigmatic quantum transport setup: an interacting quantum dot coupled to noninteracting metallic leads. Using the random phase approximation, which is exact in the limit of a large number of dot levels, we map out the zero-temperature nonequilibrium phase diagram as a function of interaction strength and applied bias. We focus our analysis on the behavior of the charge susceptibility and the current noise in the vicinity of the transition. Remarkably, despite the intrinsically nonequilibrium nature of the steady state, critical charge fluctuations admit an effective-temperature description, $T_{\mathrm{eff}}(T,V)$, that collapses the steady-state behavior onto its equilibrium form. In sharp contrast, current fluctuations exhibit genuinely nonequilibrium features: the fluctuation-dissipation ratio becomes negative in the ordered phase, corresponding to a negative effective temperature for the current degrees of freedom. These results establish current noise as a sensitive probe of critical fluctuations at nonequilibrium quantum phase transitions and open directions for exploring voltage-driven critical phenomena in quantum transport systems.

Nonequilibrium quantum physics greatly simplifies in the case of time-periodic Hamiltonians, since Floquet theory provides an analog to Bloch's theorem in the time domain. Still, the formal properties of Floquet many-body theory remain underexplored. Here, we study what happens to the uniform electron gas when a space-time periodic potential of arbitrary strength is applied, which leads to band splitting. The case of a potential traveling at constant speed is special, since the problem can be made time independent by transforming to a comoving frame. We perform linear-response theory, in the sense that we apply an additional perturbatively small but nonperiodic probing field, for which we illustrate the analogy of Fermi's golden rule and the photoemission spectrum of a many-electron system. As in the equilibrium case, the latter is related to the spectral function which is positive definite. We also analyze the parameter dependence of the controllable photoemission spectra by virtue of Floquet-Bloch engineering.

We study the dc conductivity of a two-dimensional Rashba system with an in-plane Zeeman field and delta-correlated scalar disorder. We show that, although the field deforms the two helicity Fermi contours and rotates the spin texture, it does not produce anisotropic magnetoresistance in the leading quasiclassical conductivity. The result follows from a geometric identity for the total area occupied by the two helicity sheets. A density Ward identity fixes the spin-vector part of the Born self-energy to the derivative of the total particle density with respect to the field. This derivative vanishes, because the total area enclosed by the two Rashba-Zeeman sheets is independent of the in-plane field. The Born self-energy is therefore scalar and field independent, and the quasiparticle lifetime stays isotropic. The same occupied-area identity controls transport: The leading impurity ladder reduces the current vertex to the parabolic velocity, and the diagonal intraband Kubo conductivity collapses onto the two-sheet occupied area and is field independent as well. Thus, pointlike nonmagnetic impurities produce neither angular anisotropy nor field-magnitude dependence in the leading diagonal two-sheet quasiclassical conductivity. Any residual AMR from delta-correlated disorder must originate from corrections outside this sector.