Non-Hermitian systems give rise to distinct topological phenomena, yet their manifestations at temporal interfaces characterized by abrupt changes in system parameters remain largely unexplored. Upon an abrupt alteration of the Hamiltonian in a one-dimensional non-Hermitian system, the ensuing temporal interface excites both reflected and refracted wave modes. By introducing a sublattice-symmetric Hamiltonian, this study reveals the topological effects at such temporal interfaces. We find that the reflection and refraction coefficients exhibit a topological braiding structure. This structure is directly determined by the difference in the topological invariants across the interface, establishing a bulk-edge correspondence for temporal interfaces in non-Hermitian systems. Furthermore, we propose a dynamical probe that leverages the eigenvector overlap at the temporal interface to detect topological phase transitions. These findings establish a fundamental connection between topological braiding and nonreciprocal dynamics at temporal interfaces, providing a method to explore phase transition detection and nonreciprocal phenomena in time-varying non-Hermitian systems.

We investigate a mechanism for nonergodic behavior arising from destructive interference in Fock space, leading to Fock space cages (FSCs)—exact zero-energy eigenstates localized on $O\left(1\right)$ to $O\left(L^p\right)$ configurations within an exponentially large connected Krylov sector. Unlike many-body localization or Hilbert space fragmentation, FSCs emerge from graph-theoretic interference cancellations in disorder-free kinetically constrained systems with chiral symmetry. We develop systematic algorithms that enable explicit construction of these cages in four representative models, revealing this as a universal mechanism for kinetically constrained systems with chiral symmetry. Dynamically, FSCs produce persistent plateaus in the Loschmidt echo and magnetization: return probabilities scale as $L^{-2}$ for $O\left(L\right)$ cages and remain $O\left(1\right)$ for ultralocal ones, while the magnetization saturates to $O\left(1\right)$ instead of decaying to zero. This may provide new routes for engineering long-lived nonthermal states in quantum simulation platforms.

Can superconducting order be engineered as a robust attractor of open-system dynamics in strongly correlated systems? We demonstrate this possibility by proposing a minimal dissipation-engineering protocol for the particle-hole symmetric Hubbard model. By applying a rotated quantum jump operator, specifically a locally transformed $\eta$-pair lowering operator, on a single lattice site only, we show that the Lindblad evolution autonomously pumps the system from the vacuum into a nonequilibrium steady state (NESS) exhibiting macroscopic $\eta$-pair off-diagonal long-range order (ODLRO). Crucially, this local-to-global synchronization stands in stark contrast to schemes reliant on spatially extensive reservoirs: Here, a single local dissipative seed suffices to establish long-range coherence across the entire interacting lattice system. We elucidate the underlying mechanism via three core features: Local dark-state selection, the controlled elimination of off-manifold excursions induced by hopping, and a Liouvillian invariant-subspace structure that yields an attractive fixed point with a finite dissipative gap. Furthermore, we systematically classify the stability of this NESS with respect to static disorder, and identify a wide regime in which the superconducting attractor remains robust against Hamiltonian perturbations that preserve the effective subspace structure. We also pinpoint specific perturbations that directly cause dephasing of the $\eta$-pseudospin coherence and suppress ODLRO. These findings open up a disorder-tolerant pathway for stabilizing superconducting order as a nonthermal attractor through minimal local quantum-jump control.

Magnetic topological insulators host exotic phenomena such as the quantum anomalous Hall effect and quantized magnetoelectric responses, but dynamic electrical control of their topological phases remains elusive. Here we demonstrate from first principles that spin-orbit torque enables direct electrical switching of the Néel configuration in intrinsic antiferromagnetic bilayer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, thereby reconfiguring its boundary spectrum. A symmetry-allowed interband (time-reversal even) torque persists inside the bulk gap, and deterministically reverses the Néel order and layer-resolved Chern marker without free carriers. Upon doping, both interband and intraband torques are amplified, lowering the critical electric field for switching by two orders of magnitude. Together, these results establish two complementary regimes of control: dissipationless in-gap torques without Joule heating, and enhanced current-induced torques, providing a robust route to manipulate a layer-resolved Chern marker and helical-like gapped edge modes in antiferromagnetic ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$.

We report a systematic study of the magnetic and ferroelectric properties of ${\mathrm{Co}}_3{\mathrm{TeO}}_6$ single crystals under pulsed magnetic fields up to 60 T, revealing pronounced anisotropic magnetoelectric coupling and novel ferroelectric phenomena. For $H//a$, in addition to a low-field spin-flop transition at $H_{a1}$ $\sim 16.7$ T, two additional metamagnetic transitions occur at $H_{a2}$ $\sim 18.3$ T and $H_{a3}$ $\sim 57.6$ T, which correlate with a distinct new ferroelectric phase exhibiting anomalous polarization reversal. An intriguing characteristic of this reversal is the formation of a large “∞”-shaped hysteresis loop, arising from polarization sign reversal during the H-falling sweep relative to the H-rising sweep. This ferroelectric response is highly dependent on the field-sweep history, indicating complex magnetoelectric behaviors in the system. In the case of $H//b$, successive metamagnetic transitions are observed at $H_{b1}$ $\sim 6.9$ T, $H_{b2}$ $\sim 11.5$ T, $H_{b3}$ $\sim 21.2$ T, and $H_{b4}$ $\sim 35.8$ T, with an additional transition at higher critical magnetic fields $\left(H_{b5}\right)$ above 10 K. Each transition corresponds to distinct ferroelectric phases, which exhibit varying responses to the applied bias electric field (E). In particular, the high-field ferroelectric phase above $H_{b4}$ demonstrates a robust memory effect, where both the direction and magnitude of electric polarization are retained across successive pulses of −E and +E. This suggests that the pinning of ferroelectric domain walls may prevent polarization reversal under opposing bias fields. Complementary magnetostriction measurements support the magnetization results and reveal spin-lattice coupling. Based on these comprehensive experimental findings, we construct the magnetic-field-temperature phase diagrams and investigate the underlying origin of magnetoelectric coupling in ${\mathrm{Co}}_3{\mathrm{TeO}}_6$. Our results offer valuable insights into high-field-induced ferroelectric phases and unusual magnetoelectric effects in noncollinear multiferroic systems.

Understanding how quasiparticles interact with impurities is crucial for unveiling novel properties of quantum many-body systems. A prominent example is the enhanced scattering between electrons and magnetic impurities in the low-energy limit, which gives rise to the Kondo effect. In this letter, motivated by recent developments in quantum simulation platforms, we investigate the universal behavior of long-range quantum spin chains with a single local impurity, focusing on systems that conserve the magnon number. Using effective field theory, we show that distinct classes of universal three-magnon states can emerge when the impurity-mediated two-magnon interaction is on resonance. When the long-range coupling decays as $1/r^{\alpha }$, we find that (i) for $\alpha \in (2,2.89)$, the system exhibits Efimov effects, with the $n$-th three-body binding energy $|E_{\text{3-body}}^{\left(n\right)}|$ forming a geometric series $ln|E_{\text{3-body}}^{\left(n\right)}|\sim -n(\alpha -1)\pi /s_0\left(\alpha \right)$ with a parameter $s_0\left(\alpha \right)$, (ii) for $\alpha =2$, the system shows semisuper Efimov effects with $ln|E_{\text{3-body}}^{\left(n\right)}{|\sim -(n\pi -\theta )}^2/8$ for constant $\theta$. Our theoretical prediction is validated by the numerical solution of the Skorniakov-Ter-Martirosian equation. Our results could be tested experimentally in the future on quantum simulation platforms.

Barium-rhodium silicide $\mathrm{BaRh}{\mathrm{Si}}_2$ has been successfully synthesized using a high-pressure technique at 6 GPa. X-ray Rietveld analysis and scanning transmission electron microscopy studies revealed that $\mathrm{BaRh}{\mathrm{Si}}_2$ is isostructural to $\mathrm{BaIrS}{\mathrm{i}}_2$, within the noncentrosymmetric space group $C{222}_1$ with the lattice parameters $a=14.9777\left(1\right)\AA , b=8.0517\left(1\right)\AA$, and $c=8.0551\left(1\right)\AA$. Electrical resistivity, magnetic moment, and specific-heat measurements indicate that $\mathrm{BaRh}{\mathrm{Si}}_2$ is a type-II superconductor with a critical temperature $T_{\mathrm{c}}\sim 5.1\mathrm{K}$, an upper critical field $H_{\mathrm{c}2}\left(0\right)\sim 32$ kOe, and a Ginzburg-Landau parameter ${\kappa }_{\mathrm{GL}}\sim 56$. The superconductivity is a Bardeen-Cooper-Schrieffer (BCS)-like state with moderate electron-phonon coupling ${\lambda }_{\mathrm{ep}}\sim 0.6$ and weak electron correlation ${\lambda }_{\mathrm{ee}}\sim 0.1$. Phonon mediation seems to be dominant for the Cooper pairing. The ab initio calculations revealed that $\mathrm{BaRh}{\mathrm{Si}}_2$ has three pairs of Fermi surfaces split by spin-orbit coupling. The band splitting energy is around ${\mathrm{\Delta }}_{\mathrm{ASO}}\sim 0.03$ eV near $E_{\mathrm{F}}$, which is rather smaller than that ($\sim 0.07$ eV) in $\mathrm{BaIrS}{\mathrm{i}}_2$.

We present a microscopic derivation of Usadel-type theory describing the superconductor-altermagnet hybrid structures in the dirty limit. The combined influence of the momentum-dependent exchange field and potential scattering at nonmagnetic impurities is shown to result in the appearance of the effective magnetic scattering in analogy to the Dyakonov-Perel spin-relaxation mechanism. The disorder, thus, can compensate the destructive effect of the altermagnetic exchange field on the superconducting gap, which can be probed by standard experimental techniques sensitive to the energy dependence of the density of states. The effective magnetic impurities reveal the uniaxial anisotropy determined by the Neel vector of the altermagnet. This anisotropy could be detected, e.g., by the Knight shift measurements in NMR experiments.

Achieving nonthermally and ultrafast optical control of phase transition is pivotal to developing next-generation optoelectronics. Tin selenide (SnSe) is a promising candidate with ultrafast-pulse tuning functionality due to its multiple lattice instabilities and unique in-plane ferroelectricity. Here, we report two distinct laser fluence-dependent nonthermal phase transition pathways in SnSe by using nonadiabatic molecular dynamics based on real-time time-dependent density functional theory calculation. At low laser fluence, SnSe undergoes an ultrafast all-optical switching of intralayer ferroelectricity ($P\to -P$) for bulk Pnma antiferroelectric state, where the centrosymmetric Cmcm phase acts as a structural intermediary. In contrast, high laser fluence drives a direct transition from Pnma phase to a stable and higher-symmetry Immm paraelectric phase that completely quenches the intralayer ferroelectric order. Moreover, it reveals that photoexcitation of electrons from Se $4p$ to Sn $5p$ orbitals determines the photoinduced phase transition pathways, which reshapes the potential energy surface and coherently excites interlayer shear and intralayer soft phonons. The present work not only unveils the ultrafast nonequilibrium dynamics of photoinduced phase transitions in SnSe, but also provides an efficient strategy to control in-plane polarization through an intermediary phase.

We analyze the dispersion of collective modes in a superconductor with $d\text{−}\mathrm{wave}$ symmetry of the order parameter in the presence of long-range Coulomb interaction. We use diagrammatic technique and quasiclassical theory in the Keldysh-Nambu formalism to compute longitudinal and transverse pair susceptibilities and extract from them the dispersion of the longitudinal and transverse collective mode. We show that at $T=0$ the dispersion of the transverse (plasma) mode is the same as in an $s$-wave superconductor, but at a finite $T$ it is softer and has a much larger decay rate due to the partial screening of the Coulomb potential by nodal quasiparticles. We show that the dispersion of the longitudinal mode depends on the direction of momentum with respect to the positions of the nodes of the $d\text{−}\mathrm{wave}$ gap, while the decay rate of this mode does not depend on momentum. We discuss experimental implications of our results.

Light-induced absorption change of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) was investigated using femtosecond transient absorption spectroscopy in the visible and near-infrared regions from 0.94 to 2.85 eV. It was found that the photoexcitation of chemical polarons with the near-infrared pulse (photon energy of 1.55 eV) results in a broad absorption increase over these spectral regions at the time origin. This absorption increase was explained by the ultrafast formation of bipolarons in the PEDOTs. The exciton formation with the near-ultraviolet pulse (photon energy of 3.10 eV) induced an absorption increase from 0.95 to 1.48 eV and an absorption decrease from 1.57 to 2.85 eV. This spectral behavior was explained by the sequential bipolaron formation caused by the exciton relaxation via excitation of a neighboring chemical polaron. This study revealed the relaxation processes of excited chemical polarons and excitons in doped conjugated polymers.

A two-dimensional second-order topological insulator exhibits topologically protected zero-energy states at its corners. In the literature, the breathing kagome lattice with nearest-neighbor hopping is often mentioned as an example of a two-dimensional second-order topological insulator. Here, we show by explicit construction that the corner states of the breathing kagome lattice can be removed by a continuous change of the hopping parameters, without breaking any of the model's symmetries, without closing bulk and boundary gaps, and without introducing hopping terms not present in the original model. Furthermore, we topologically classify all three-band lattice models with the same crystalline symmetries as the breathing kagome lattice and show that though none of the phases have protected zero-energy corner states, some of the phases are obstructed atomic limits which exhibit a filling anomaly.

Depending on the lattice geometry, the prototypical nearest-neighbor (NN) tight-binding model for free fermions gives rise to particle-hole symmetric emergent Dirac liquids, Fermi liquids, and (quasi)flat bands near half filling or zero energy on (bipartite) Euclidean and hyperbolic lattices, respectively, embedded on flat and negatively curved spaces. Such noninteracting electronic fluids are characterized by a vanishing, a finite, and a diverging density of states near the half-filling, respectively. Here, we outline a general principle of realizing non-Hermitian (NH) generalizations of these scenarios in which the resulting NH operator features an all-real eigenvalue spectrum over an extended NH parameter regime where all the single-particle states remain sharp and filling factor is well defined. Most importantly, such a construction reduces the bandwidth of noninteracting systems without altering the characteristic scaling of the density of states close to the zero energy, thereby triggering the ordering propensity toward the nucleation of a family of spontaneous symmetry-breaking quantum phases, named commuting-class masses, at weaker interactions. We name this phenomenon ‘‘non-Hermitian catalysis of spontaneous symmetry breaking’’ that hinges on a robust and universal algebraic criterion, ultimately liberating this mechanism from the burden of the underlying lattice specification as well as the dimensionality of the system. We establish the NH catalysis of commuting-class masses from the numerical self-consistent solutions of the charge-density-wave and spin-density-wave orders at weaker (in comparison to the counterparts in conventional or Hermitian systems) NN Coulomb and on-site Hubbard repulsions, respectively, obtained by decomposing them in the Hartree channel when combined with the biorthogonal quantum mechanics on NH Euclidean and hyperbolic lattices in which the non-Hermiticity results from an imbalance of the hopping amplitudes between the sites of two sublattices in the opposite directions. These two ordered states correspond to staggered patterns of average electronic density and spin between the NN sites, respectively, and both cause insulation in half-filled systems. We discuss the scaling of the associated mass gaps near the zero energy with the non-Hermitian parameter, showing excellent agreement with analytical predictions, and also address the finite-size scaling of the order parameters specifically on hyperbolic lattices with open boundary conditions. We conclude with an outline of possible experimental platforms to test our concrete theoretical predictions.

Flat-band breathing kagome lattices host strong Coulomb interactions that can fundamentally alter the nature of their low-energy degrees of freedom. Here we show, using first-principles Density Functional Theory-GW–Bethe-Salpeter theory, that single-layer ${\mathrm{Nb}}_3{\mathrm{Cl}}_8$ realizes a spin-triplet Frenkel exciton with exceptionally large binding energy, leading to a dark excitonic Mott insulating phase. The lowest dark exciton lies 0.14 eV below the quasiparticle gap, while bright excitons appear at 0.94 and 1.21 eV with binding energies of 2.05 and 1.77 eV. Because these excitons are localized and possess a strong intrinsic out-of-plane electric dipole, the system hosts two independent excitonic degrees of freedom: a spin-1 moment and an out-of-plane electric dipolar orientation. Their collective behavior is described by an effective Hamiltonian on the triangular lattice, which naturally supports antiferromagnetic and ferroelectric ordering tendencies. Our results thus establish a correlation-driven route to multiferroicity in flat-band frustrated lattices and identify single-layer ${\mathrm{Nb}}_3{\mathrm{Cl}}_8$ as a candidate multiferroic dark excitonic Mott insulator.

We investigate the ground-state phase diagram of the $S$ = 1/2 XXZ model on the two-dimensional Shastry-Sutherland lattice using exact diagonalization (ED), density-matrix renormalization group (DMRG), and cluster mean-field theory (CMFT) with DMRG as a solver. In the isotropic case ($\mathrm{\Delta }=1$), CMFT results reveal an intermediate empty plaquette (EP) phase that has a lower energy than the full plaquette (FP) phase. However, due to mean-field artifacts, CMFT alone is not suitable for accurately determining phase boundaries. Therefore, we combined three methods to map out the reliable phase diagram. Our calculations show that the EP phase narrows as $\mathrm{\Delta }$ deviates from unity and eventually vanishes. More importantly, we identify a spiral phase at small $\mathrm{\Delta }$, which has not been reported in previous studies. This phase is clearly captured by DMRG simulations on long cylindrical geometries. The competition between the EP, spiral, and $xy$-AFM phases near their boundaries provides a plausible explanation for the emergent spin-liquid-like behavior in ${\mathrm{Pr}}_2{\mathrm{Ga}}_2{\mathrm{BeO}}_7$, while shedding new light on the role of XXZ anisotropy in the Shastry-Sutherland XXZ model.

Hopf terms are topological theta terms that are associated with a host of interesting physics, including anyons, statistical transmutation, chiral edge states, and the spin quantum Hall effect. Here, we show that Hopf terms can appear in two-dimensional metals without spin-orbit coupling in the vicinity of spin-ordered phases. In their vicinity, their spinlike order parameters have a finite amplitude, but fluctuating orientation. When both a magnetic and a spin loop-current order parameter fluctuate in the system, we show that the phase is governed by the Hopf term and realizes a Hopf symmetry protected topological phase. This phase is protected by the unbroken $\mathrm{SU}\left(2\right)$ spin rotation symmetry, is gapped in the bulk, has chiral gapless edge states, and its spin-Hall conductance is quantized. Lattice models that realize this phase are introduced. In addition, we provide an elementary proof that the $\theta$ angle of the Hopf term must be quantized to multiples of $\pi$ in nonrelativistic systems, thereby precluding anyonic skyrmions in condensed matter systems.

This work provides a comprehensive study of charge-2 Dirac points (C2 DPs) in spinless systems, systematically analyzing their emergence and properties based on the 230 space groups and corresponding material candidates. By deriving the necessary symmetry constraints, we establish that the stabilization of C2 DPs requires two independent screw rotations that anticommute with each other, along with time-reversal symmetry. This symmetry-based framework allows us to identify only nine space groups capable of hosting C2 DPs, offering a clear guideline for identifying material candidates. Through high-throughput calculation, and based on the latest Materials Project database, we identify 57 candidate materials, including 47 nonmagnetic (NM) and 10 ferromagnetic (FM) systems, that exhibit C2 DPs at high-symmetry points or paths. To further explore the intrinsic properties of C2 DPs and their topological phase transitions, we select two representative materials: the NM material ${\mathrm{IO}}_3$ and the FM material ${\mathrm{PH}}_5{\mathrm{N}}_2{\mathrm{O}}_4$. Our analysis reveals that C2 DPs at high-symmetry points are symmetry-essential band crossings, which transform into pairs of Weyl points (WPs) under symmetry-breaking conditions. C2 DPs on high-symmetry paths are accidental crossings, which can be gapped without requiring symmetry breaking. These findings not only advance the understanding of C2 DPs in spinless systems but also provide a robust platform for experimental exploration and theoretical studies of topological phase transitions, paving the way for future discoveries in the field of topological materials science.

Developing effective approaches to modulate the nonlinear optical (NLO) responses of materials is of great importance to design novel optoelectric devices. Recent studies have reported two distinct pressure-induced second-harmonic generation (SHG) modulation behaviors in $\mathrm{NbO}{\mathrm{I}}_2$, with one enhanced and the other suppressed. These observations have sparked considerable interest in the underlying physical mechanism. Using first-principles calculations, we have declared the structure evolution path of $\mathrm{NbO}{\mathrm{I}}_2$ under pressure, where spontaneous polarization decreases, and the Peierls distortion ratio holds. The SHG susceptibility exhibits a global reduction across all frequencies due to suppressive quantum geometric quantities. On the other hand, a series of artificial structures with different Peierls distortion ratios was designed to explain the SHG boost in experiments, which is attributed to modified electronic dispersion relations. In addition, by applying uniaxial strain to the polarization axis, our results show that optical transition probability overtakes the shift vector as the primary contributor in polarization-dependent SHG. Hence, we demonstrate tunable SHG response governed by distinct microscopic mechanisms in the $\mathrm{NbO}{\mathrm{I}}_2$ system. Our findings not only contribute to clarifying different pressure-induced SHG behaviors in $\mathrm{NbO}{\mathrm{I}}_2$ but also deepen our understanding of SHG evolution under external fields.

Dynamical mean-field theory computations of the electron self-energy of the Hubbard-Holstein model as a function of electron-phonon and electron-electron interactions are analyzed to gain insight into the dependence of electron-phonon couplings on correlation strength in quantum materials. We find that the electron-phonon interaction is strongly suppressed by electronic correlations, while electron-electron correlation effects at Fermi liquid scales are only weakly modified by coupling to phonons, with phonon-induced modifications most evident at high frequencies on the order of the electronic bandwidth. Implications for beyond-density functional theories of the electron-phonon interaction are discussed.