Dimensionality critically governs correlated states, often inducing emergent ground states in reduced dimensions. While ${\mathrm{VSe}}_2$ has been studied extensively, its monolayer ground state remains controversial. Here, we resolve these issues by investigating the thickness-dependent evolution of charge density waves (CDWs) and magnetism in ${\mathrm{VSe}}_2$. Using angle-resolved photoemission spectroscopy, we observe pronounced temperature-dependent band reconstruction uniquely emerging in bilayer and monolayer ${\mathrm{VSe}}_2$, in sharp contrast to bulk and multilayer ${\mathrm{VSe}}_2$. While a $\sqrt{3}\times \sqrt{7}$ CDW accounts for the reconstructed band topology, it fails to explain the global suppression of spectral weight at low temperature. Instead, DFT calculations suggest that a coupled $\sqrt{3}\times \sqrt{7}$ spin density wave $\left(\mathrm{SDW}\right)+\mathrm{CDW}$ state can quantitatively account for all key experimental observations. These results are consistent with a thickness-driven crossover to a coupled $\mathrm{SDW}+\mathrm{CDW}$ state, establishing ${\mathrm{VSe}}_2$ as a tunable platform for exploring intertwined spin-charge orders in two-dimensional quantum materials.

Even-denominator fractional quantum Hall (FQH) states can be viewed as topological superconductors of composite fermions, supporting a charged chiral mode and $|{\mathcal{C}}_{cf}|$ neutral Majorana modes set by the Chern number ${\mathcal{C}}_{cf}$. Despite ongoing efforts, distinguishing the many competing paired phases remains an open problem. In this work, we propose a unified theory of charge transport across a quantum point contact for general paired FQH states described by an $\text{SO}{\left(N\right)}_1\times U\left(1\right)$ conformal field theory. We derive the boundary effective action for an arbitrary number of Majorana fermions $N=|{\mathcal{C}}_{cf}|$ and develop a nonperturbative instanton approximation to describe tunneling processes. We establish a weak-strong duality relating strong quasiparticle tunneling to weak electron tunneling. We calculate the scaling dimensions of the tunneling operators and demonstrate that while the weak-coupling fixed point is generally unstable, the strong-coupling fixed point is stable for physically relevant filling fractions and number of Majorana fermions. These transport exponents provide a distinct experimental fingerprint to identify the topological phases of even-denominator FQH states.

We introduce a tree tensor network (TTN) impurity solver that enables highly efficient and accurate real-time simulations of quantum impurity models. By decomposing a noninteracting bath Hamiltonian into a Cayley tree, the method provides a tensor-network representation that naturally captures the multiscale entanglement structure intrinsic to impurity–bath systems. This geometry differs from conventional chain-based mappings and yields a substantial reduction of entanglement, allowing accurate ground-state properties and long-time dynamics to be captured at significantly lower bond dimensions. Benchmark calculations for the single-impurity Anderson model demonstrate that the TTN solver achieves markedly enhanced resolution of real-frequency spectral functions, without invoking analytic continuation. This impurity solver provides a balanced, scale-uniform description of impurity physics and offers a versatile approach for real-time dynamical mean-field theory and related applications involving quantum impurity models.

Ultrafast thermal switches are essential for thermal management in next-generation solid-state technologies, including high-speed chipsets, thermal logic circuits, and on-chip lasers. However, conventional thermal switches fail to satisfy the stringent requirements for picosecond-scale response times, whereas existing laser-triggered thermal switches that rely on conformational rearrangements suffer from inherent limitations in reliability and operational lifetime. To overcome these challenges, we propose a laser-driven ultrafast thermal switching in antiferromagnetic monolayer MnSe by using real-time time-dependent density functional theory and the Boltzmann transport equation. This work reports the timescale of complete laser-induced demagnetization. Specifically, a laser pulse with a fluence of $5.1\mathrm{mJ}/{\mathrm{cm}}^2$ triggers an ultrafast demagnetization between the two Mn sublattices in monolayer MnSe via the interplay of optical intersite spin transfer and phonons, resulting in a transient nonmagnetic state within approximately 80 fs. The transient magnetic transition from antiferromagnetism to nonmagnetism drastically suppresses thermal conductivity from 8.33 to 0.64 W/(m K), corresponding to a 13-fold reduction. This modulation primarily arises from demagnetization-enhanced phonon scattering, which is dominated by four-phonon recombination and redistribution processes involving the in-plane acoustic phonon branches. These findings establish two-dimensional magnetic materials as a viable platform for ultrafast thermal switching.

Symmetry provides powerful nonperturbative constraints in quantum many-body systems. A prominent example is the Lieb-Schultz-Mattis (LSM) anomaly—a mixed 't Hooft anomaly between internal and translational symmetries that forbids a trivial symmetric gapped phase. In this work, we investigate lattice translation operators in systems with an LSM anomaly. We construct explicit lattice models in two and three spatial dimensions and show that, after gauging the full internal symmetry, translation becomes noninvertible and fuses into defects of the internal symmetry. The result is supported by the anomaly inflow in view of topological field theory. Our work extends earlier one-dimensional observations to a unified higher-dimensional framework and clarifies their origin in mixed anomalies and higher-group structures, highlighting a coherent interplay between internal and crystalline symmetries.

Understanding the role of holes in energy transport mechanisms and determining electron intervalley scattering times is crucial for optimising Ge-based optoelectronic devices such as transistors, photodetectors, power devices, and light emitters. By employing our recently developed, ultrafast 20-fs resolution ellipsometer, we demonstrate that the absorption (${\varepsilon }_2$) in various types of Ge continues to decrease in the first picosecond after optical excitation, proving that the revival of the absorption is limited by the intrabandlike relaxation of holes (near the Γ point), instead of the intervalley scattering of the electrons. The observed decay times depend on the probing photon energies attributed to the different lifetimes of the holes in the light, split-off and heavy-hole bands. With gradually decreasing degree of crystallinity of our single crystalline, semicrystalline and amorphous Ge samples, the recovery times also decrease, which is related to the appearance and intensification of real-space scattering events over reciprocal space scattering. There is excellent correspondence for electron relaxation times for different samples with our two-temperature model, which is thoroughly analyzed via band-structure calculations. Our results contribute to the understanding of the excitation and decay processes in not only crystalline semiconductors, but also semicrystalline and amorphous semiconductors, resolving corresponding debates.

Bound states in the continuum (BICs) constitute a class of optical resonances characterized by ultrahigh quality (Q) factors, which promise to significantly enhance light-matter interactions. However, their practical performance is often degraded by the presence of topological defects in momentum space. We propose a “momentum-space purification” scheme for silicon-based metasurfaces. Annihilating oppositely charged accidental BICs eliminates topological singularities around the Γ-point symmetry-protected BIC (SP-BIC), flattening the local Berry-curvature distribution and markedly improving robustness against structural perturbations. This purification eliminates parasitic scattering channels, dramatically boosting third-harmonic generation (THG). Notably, the THG conversion efficiency exhibits a consistent transition from $\eta \propto Q^2$ to $\eta \propto Q^4$ scaling across all postpurification parameters, a signature of a fundamental change driven by topological engineering and a step toward robust nonlinear photonic devices.

The roles of boron (B)‐layer topology in governing the stability, bonding, mechanical behavior, and pressure‐driven structural evolution of tungsten diboride (${\mathrm{WB}}_2$) were investigated using first-principles calculations, in which three representative polymorphs (hp3‐, hp6‐, and $\mathrm{hp}12\text{−}{\mathrm{WB}}_2$) were involved. By combining the analyses of formation enthalpy, elastic properties, ideal cleavage, and mechanical responses under shear and under tensile/compressive loading, and electronic structures, direct correlations between B-layer topology, bonding characteristics, and mechanical behavior were established. It was found that hp6-${\mathrm{WB}}_2$, with fully corrugated B layers, is the most stable polymorph in the ideal defect-free limit and exhibits the highest elastic stiffness and the strongest resistance to cleavage, basal shear, and tensile deformation. In contrast, $\mathrm{hp}3\text{−}{\mathrm{WB}}_2$, containing planar B layers, shows the lowest stiffness and hardness and a relatively weak tension‐compression asymmetry; and $\mathrm{hp}12\text{−}{\mathrm{WB}}_2$, composed of alternating planar and corrugated B layers, displays intermediate stability and heterogeneous mechanical behavior, with high compressive resistance but reduced tensile resistance. Electronic‐structure analysis showed that B‐layer topology modulates the directionality of B–B bonding and the degree of B‐p/W‐d hybridization, thereby controlling load-transfer pathways and failure mechanisms. Under compression, $\mathrm{hp}12\text{−}{\mathrm{WB}}_2$ does not transform into an hp6-like structure prior to instability, whereas hp6-${\mathrm{WB}}_2$ exhibits a pronounced tendency toward the planarization of B layers. These results demonstrate that B‐layer topology governs not only the stability and mechanical behavior but also topology-dependent deformation pathways, providing an insight into structure–property relationships in layered transition-metal borides.

We determine the finite-temperature phase diagram of a one-dimensional disordered Bose gas using bosonization and the nonperturbative functional renormalization group (RG). We discuss two different scenarios, based on distinct truncations of the effective action. In the first scenario, the Bose glass is destabilized at any finite temperature, giving rise to a normal fluid. Nevertheless, one can distinguish a low-temperature glassy regime, where disorder plays an important role on intermediate length and time scales, from a high-temperature regime, where disorder becomes irrelevant. In the second scenario, below a temperature $T_c$, the RG flow exhibits a singularity at a finite value of the RG momentum scale. We propose that this singularity signals a lack of thermalization and the existence of a localized phase for $T<T_c$. We provide a description of this low-temperature localized phase within a droplet picture and highlight a number of possible similarities with characteristics of many-body localized phases, including nonthermal behavior, avalanche instabilities and many-body resonances, the structure of the many-body spectrum, and slow dynamics in the ergodic phase. The normal fluid above $T_c$, and below a crossover temperature $T_g$, exhibits glassy properties on intermediate scales.

While phases and phase transitions are conventionally described by local order parameters in real space, we present a unified framework that characterizes phase transitions through the geometry of configuration space, defined by the statistics of pairwise distances $r_H$ between configurations. Focusing on the concrete example of Ising spins, we establish crucial analytical links between this geometry and fundamental real-space observables, i.e., the magnetization and two-point spin-correlation functions. This link unveils the universal scaling law in the configuration space: the standard deviation of the normalized distances exhibits universal criticality as $\sqrt{\mathrm{Var}\left(r_H\right)}\sim L^{-2\beta /\nu }$, provided that the system satisfies $4\beta /\nu <d$. We validate this scaling with stochastic series expansion quantum Monte Carlo simulations of the transverse-field Ising model (TFIM). Furthermore, we propose configuration-space diagnostics that go beyond local real-space observables. First, the distribution probability $P\left(r_H\right)$ parametrized by the transverse field $h$ forms a one-dimensional manifold. Information-geometric analyses, particularly the Fisher information defined on this manifold, successfully pinpoint the TFIM phase transition, regardless of the measurement basis. Second, for the Su-Schrieffer-Heeger Heisenberg model, a parity index derived from $P\left(r_H\right)$ successfully characterizes the symmetry-protected topological phase and its transition. Our work establishes configuration-space geometry as a novel perspective on quantum criticality, revealing how macroscopic universal phenomena are encoded within its global statistical features.

Rare-earth compounds, such as Gd-based intermetallics, exhibit strong magnetocaloric effects (MCEs) and emerge as promising candidates for technological applications in magnetic refrigeration and cryogenics. In this work, we conducted a combined experimental and theoretical investigation of the magnetocaloric properties of the orthorhombic ${\mathrm{GdNi}}_4\mathrm{Al}$ crystal. The experimental measurements were performed at ambient pressure, while the effects of hydrostatic pressure up to 20 GPa were investigated theoretically. From $\mathrm{DFT}+U$ and Monte Carlo (MC) simulations, the exchange parameters were determined, and their dependence on pressure was analyzed using different generalized gradient approximations (PBE, PBESol, and AM05). The results show that the exchange interaction between the nearest and next-nearest neighbors are the main factors responsible for the sensitivity of the critical temperature to pressure, while the exchange interaction between next-next-nearest neighbors remains practically unchanged throughout the investigated pressure range. Both mean-field models and MC simulations predict a linear decrease in critical temperature at low pressures, consistent with the Ruderman-Kittel-Kasuya-Yosida coupling mechanism. The MCE, characterized by the maximum entropy variation and the refrigerant capacity, proves to be remarkably stable under compression, remaining practically independent of pressure. Our results demonstrate the structural and magnetic robustness of ${\mathrm{GdNi}}_4\mathrm{Al}$ under extreme conditions and offer a microscopic view of the mechanisms of modulation of pressure-induced MCEs in rare-earth intermetallics.

Building upon the spin-1/2 Kitaev model on a honeycomb lattice, the Yao-Lee spin-orbital model provides exactly solvable quantum spin liquids with potentially better stability against perturbations due to the additional degree of freedom. Recently, the microscopic mechanism underlying the Yao-Lee interaction in honeycomb materials has been uncovered, leading to an extended Kitaev-Yao-Lee spin-orbital model when the celebrated Kugel-Khomskii interaction is included. Numerical studies of this model identified various disordered phases, including a broad region of the nematic phase that was reminiscent of a spin-orbital liquid. Here, we investigate the origin and stability of this nematic phase via thermal and quantum fluctuations using classical Monte Carlo simulations and a generalized spin-wave theory appropriate for the spin-orbital model. We demonstrate that the additional spin-orbital degree of freedom gives rise to strong thermal and quantum fluctuations in spin-orbital models, providing insight into the emergence of disordered phases.

We study the dynamics of the longitudinal collective mode in an unconventional superconductor. For concreteness, we assume that the superconductor is described by a $d$-wave order parameter with $d_{x^2-y^2}$ symmetry. After the superconductor has been suddenly subjected to a perturbation at time $t=0$, the order parameter exhibits a peculiar oscillatory behavior, with the amplitude of the oscillations slowly decaying with time in a power-law fashion. Assuming that the initial perturbation is weak, we use a formalism based on the quasiclassical approach to superconductivity to determine both the frequency of the oscillations as well as how fast these oscillations decay with time by evaluating the time dependence of the pairing susceptibility. We find that the frequency of the oscillations is given by twice the value of the pairing amplitude in the antinodal direction and its amplitude decays as $1/t^2$. The results are also verified by a direct calculation of the order parameter dynamics by numerically solving the equations of motion for the Anderson pseudospins.

We present a systematic comparison of the real-time Dyson expansion (RTDE) with established nonequilibrium Green's function (GF) approaches for simulating driven, interacting quantum systems. Focusing on density matrix dynamics, time-off-diagonal GFs, and time-resolved photoemission spectra, we benchmark RTDE against fully self-consistent Kadanoff-Baym equation (KBE) calculations, the generalized Kadanoff-Baym ansatz, and exact diagonalization for small systems using second-order many-body perturbation theory. Using a driven two-band Hubbard model, we show that mean-field single-particle density matrix trajectories provide a reliable baseline for RTDE across a broad range of interaction strengths and excited-carrier populations. Further, RTDE accurately captures correlation effects in the GFs, including long-lived oscillations and revivals that are strongly suppressed by the overdamping inherent to self-consistent KBE schemes. As a consequence, RTDE resolves rich nonequilibrium spectral structure in time-resolved photoemission, such as interaction- and population-dependent quasiparticle splittings and band gap renormalization, which are largely washed out in self-consistent approaches yet are present in exact solutions. Our results demonstrate that RTDE bridges the gap between mean-field propagation and full two-time KBE simulations, retaining favorable linear scaling while capturing essential dynamical correlations relevant for ultrafast spectroscopy.

In a nondegenerate n-type semiconductor, the electron conduction at low temperatures is due to the Efros-Shklovskii variable-range hopping in a narrow donor energy band separated from the conduction band by the donor ionization energy. As the donor density reaches the critical density for the Mott transition ($n_{\text{c}}$), the donor ionization energy turns to zero and the electrons released from the donors form a degenerate gas in the conduction band. Usually, the Fermi energy of the degenerate gas exceeds the Anderson mobility edge and the Mott transition is therefore accompanied by a change of the hopping conductance to the metallic conductance. Here we study the highly Si-doped $\beta –\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ semiconducting films by measuring the conductivity, Hall effect, Seebeck coefficient, and optical absorption spectrum, as well as by structural and chemical characterization. We vary the density of the electrically active Si donors ($n$) from low values up to $n=n_{\text{c}}$ (we show that $n_{\text{c}}=5.7\times {10}^{18}{\text{cm}}^{-3}$) and slightly above. We observe the donor-density-driven Mott transition from the nondegenerate disordered semiconductor to a degenerate disordered metal with Fermi energy well below the mobility edge. At low temperatures on the semiconducting side of the Mott transition ($n<n_{\text{c}}$), we observe the Efros-Shklovskii hopping with characteristic energy $\propto {\left(1-n/n_{\text{c}}\right)}^2$, as predicted by theory. Similarly, the donor ionization energy tends to diminish for $n\to n_{\text{c}}$ and is likely proportional to the same factor. On the metallic side of the Mott transition ($n>n_{\text{c}}$) the low-temperature transport changes from the Efros-Shklovskii hopping to the Mott variable-range hopping, manifesting the closure of the Efros-Shklovskii Coulomb gap at the Mott transition. At high temperatures, the conductance still exhibits localized transport for both $n>n_{\text{c}}$ and $n<n_{\text{c}}$, but, surprisingly, in the latter case with a linear temperature dependence as $n$ approaches $n_{\text{c}}$. We identify this transport regime as the anomalous variable-range hopping of the nondegenerate conduction electrons moving in disorder, which does not originate from Si doping. Our optical data indeed show that the conduction-band states are localized by extra disorder due to the oxygen vacancies, which is also confirmed by the chemical composition data. Finally, the room-temperature Seebeck data confirm the nondegenerate electron transport and also indicate merging of the donor band into the conduction band at the Mott transition.

Identifying two-dimensional heterostructures with exceptional electronic and optical properties remains an active area of research in advanced optoelectronics. Here, we present a comprehensive first-principles investigation of the electronic, optical, and excitonic properties of a ${\mathrm{MoTe}}_2$/CrSBr van der Waals heterostructure using density functional theory combined with fully relativistic GW and Bethe-Salpeter equation calculations. The close lattice matching between the two monolayers enables the formation of stable heterobilayers with two inequivalent interfaces (Te-S and Te-Br) arising from the Janus nature of CrSBr. Both interfaces are dynamically and thermally stable and exhibit type-II band alignment with a direct quasiparticle gap, promoting efficient spatial separation of electrons and holes. The heterostructure hosts interlayer excitons with lifetimes ($18–45\mathrm{ps}$), significantly longer than those of the intralayer excitons in the isolated ${\mathrm{MoTe}}_2$ (3.6 ps) and CrSBr (8.1 ps) monolayers. Moreover, the optical gap, exciton binding energy, and exciton lifetime of the heterostructure are strongly modulated by the built-in electric field associated with the Janus layer. These results establish the ${\mathrm{MoTe}}_2$/CrSBr heterostructure as a versatile platform for engineering long-lived interlayer excitons and highlight its potential for next-generation optoelectronic and light-harvesting applications.

Strong light-matter interactions are central to advancing next-generation photonic technologies. However, the theoretical tools currently employed often fall short of accurately modeling highly dissipative systems. Traditional Hermitian approximations, which treat plasmon-exciton coupling with real-valued strengths, fail to capture defining experimental signatures such as asymmetric spectral line shapes and complex triplet structures. We address this limitation by introducing a non-Hermitian coupling theory built upon the quasinormal mode formalism for coupled plasmon-exciton systems. This approach achieves a complete theoretical description by intrinsically and self-consistently incorporating the physical realities of material dispersion, absorption, and radiation loss. By constructing a multimode, non-Hermitian Hamiltonian without fitting parameters, we directly derive hybridized eigenstates from complex-valued coupling strengths. This framework provides a unified and quantitative interpretation of strong-coupling features, offering the essential physical insights necessary for engineering truly dissipative, high-performance nanophotonic devices.