Monolayer ${\mathrm{SnS}}_2$ has emerged as a promising visible-light photocatalyst for photoelectrochemical applications, owing to its strong optical absorption in the visible range and excellent chemical stability. Despite its reduced dimensionality—where excitonic effects are expected to be pronounced—comprehensive theoretical investigations of bound excitons in this material remain scarce. Notably, unlike most two-dimensional hexagonal crystals, monolayer ${\mathrm{SnS}}_2$ exhibits its lowest single-particle transition at the $M$ point of the Brillouin zone (BZ). Here, the electronic valence bands form a saddle point while conduction states display a minimum with pronounced anisotropy, creating a distinctive band topology whose impact on optical excitations we systematically explore. In this work, we present a first-principles study of bound excitons in monolayer ${\mathrm{SnS}}_2$ based on state-of-the-art many-body perturbation theory, employing the $\mathit{GW}$ approximation and the Bethe–Salpeter equation. We analyze how band symmetry and anisotropy shape the excitonic wave functions and transition dipole moments. By resolving the exciton dipoles in momentum space for different linear light polarizations, we demonstrate that linearly polarized light lifts the $C_3$ rotational symmetry relating the three inequivalent $M$ points, giving rise to three linearly independent excitonic states. This polarization-selective coupling, previously identified for saddle points in graphene, is achieved in ${\mathrm{SnS}}_2$ for bound excitons and provides a potential route toward state encoding schemes in valleytronics applications.

The average subsystem trace distance has been proposed as an indicator of quantum many-body chaos and integrability. However, evaluating it presents two main difficulties: high computational cost for large systems and ambiguities in defining and ordering eigenstates in integrable systems. In this work, we develop an efficient algorithm to compute the Bures distance between fermionic Gaussian states, enabling access to larger system sizes. Using this method, we calculate the average subsystem Bures distance for eigenstates in the spin-1/2 transverse-field Ising chain and the Dirac fermion formulation of the quadratic Sachdev–Ye–Kitaev (Dirac ${\mathrm{SYK}}_2$) model, as well as for random pure fermionic Gaussian states. To handle degeneracy in the Ising chain, we consider simultaneous eigenstates of all local conserved charges and employ these charges to systematically order degenerate states. Our results are consistent with the earlier conjecture of linear growth with subsystem size. We show that the distinct scaling of the average subsystem distances in chaotic versus integrable systems originates from discontinuities of local conserved charges across the spectrum in integrable models. For the Dirac ${\mathrm{SYK}}_2$ model and random pure Gaussian states, we obtain similar results for the average subsystem distances, which do not show a linear increase.

The prototypical Mott-Hubbard insulator ${\mathrm{LaVO}}_3$ undergoes a structural phase transition accompanied by the onset of spin and orbital ordering below 140 K. By combining ultrafast optical pump-probe spectroscopy and two-dimensional electronic spectroscopy, we investigate the interplay between fluctuations of the local spin and orbital order parameter and the lifetime of high-energy electron-hole excitations. Specifically, we demonstrate that the pump-induced perturbation of the order parameter leads to a change of the Hubbard exciton decoherence time and, consequently, of its homogeneous linewidth. Dynamical mean-field theory calculations confirm that the exciton scattering rate is crucially affected by the degree of order of the spin and orbital lattices in ${\mathrm{LaVO}}_3$. Our results demonstrate that multi-dimensional ultrafast optical spectroscopy can be used to track the dynamics of the order parameter, thus opening new routes in the study of correlated quantum materials characterized by intertwined orders.

We have investigated the orbital-dependent electronic states of ${\mathrm{Cd}}_6\mathrm{Ce}$, a prototype of strongly correlated rare-earth-based Tsai-type quasicrystals and approximants (ACs) by soft and hard x-ray photoemission spectroscopy. Our results reveal that the $4f$ orbitals are predominantly hybridized with the valence-band electrons far from the Fermi level ($E_F$), in sharp contrast to the hybridization with conduction electrons at $E_F$ seen for the intermetallic Ce-based compounds. This anomalous hybridization should be taken into account in discussing the unresolved magnetic ground state in ${\mathrm{Cd}}_6\mathrm{Ce}$. These findings suggest that Cd-based ACs, some of which show the multistep magnetic transitions, could provide a new platform for investigating novel magnetic properties that cannot be understood within the conventional framework of hybridization at $E_F$.

The quantum anomalous Hall (QAH) effect is conventionally understood to exist only in Chern insulators, while a recent study has shown that ferromagnetic metals can also host the QAH effect. Between insulators and metals, we demonstrate that QAH can persist even in a chiral semimetal, where conduction and valence bands touch at zero energy. Transport calculations demonstrate that the Hall conductivity of such a system can be quantized in the presence of dephasing. Interestingly, its longitudinal conductivity remains finite and exhibits semimetallic behavior, in contrast to Chern insulators. This unusual transport behavior originates from the quantization of the Berry curvature integral over occupied states and the semimetallic band structure. This chiral semimetal can transition into a Chern insulator, accompanied by the vanishing of longitudinal conductivity and a reduction of the intrinsic length scale of the Hall response. Our results extend the concept of QAH and uncover the semimetallic QAH transport signatures.

We investigated the energy gap of the incommensurate charge density wave (CDW) in $1T\text{−}{\mathrm{VSe}}_2$ using scanning tunneling microscopy/scanning tunneling spectroscopy. We found that the dip structure observed near 0 mV in the tunneling spectrum for the CDW state was absent just above the CDW transition temperature. Moreover, we observed a spatial variation of the tunneling spectrum, which suggests that the periodic modulation of the electronic local density of states due to the CDW is inverted near $E_{\mathrm{F}}$. Based on these results, we conclude that the incommensurate CDW gap in ${\mathrm{VSe}}_2$ opens near $E_{\mathrm{F}}$.

Phononic higher-order topology in two-dimensional crystalline materials has attracted significant interest in recent years. Compared with their two-dimensional counterparts, three-dimensional crystalline materials can host more diverse higher-order topological phases. However, research on phononic higher-order topology in three-dimensional crystalline materials remains limited. In this work, we reveal multiple phononic higher-order topological states in the three-dimensional crystalline materials ${\mathrm{Al}}_4{\mathrm{H}}_{12}$ and ${\mathrm{Zr}}_2{\mathrm{Ti}}_4{\mathrm{H}}_8$, in which the phononic higher-order topology can be characterized by bulk polarization. In the one-dimensional nanorods of ${\mathrm{Al}}_4{\mathrm{H}}_{12}$ and ${\mathrm{Zr}}_2{\mathrm{Ti}}_4{\mathrm{H}}_8$, the phonon topological states are localized at the surfaces and hinges. In zero-dimensional nanoparallelepipeds of ${\mathrm{Al}}_4{\mathrm{H}}_{12}$ and ${\mathrm{Zr}}_2{\mathrm{Ti}}_4{\mathrm{H}}_8$, phonon topological surface states, second-order topological hinge states, and third-order topological corner states coexist. Our work extends the dimensional scope of phononic higher-order topology in crystalline materials and paves the way for future explorations of phonon topological states.

We numerically investigate second harmonic generation (SHG) in plasmonic metasurfaces composed of periodically arranged vertical split-ring resonators. By tuning a height scaling parameter $\delta$, a continuous transition from localized surface plasmon resonances to nonlocal collective modes dominated by trapped surface plasmon polaritons was observed. Such an evolution enables systematic control over radiative and dissipative losses, resulting in a significantly enhanced $Q$ factor for both bright (in-plane resonance) and dark (out-of-plane resonance) modes. In the localized regime, SHG from bright modes is limited by strong radiation loss, while in the nonlocal regime, field delocalization suppresses nonlinear interactions. We identify an optimal crossover regime where a balance between field confinement (local) and radiation suppression (nonlocal) maximizes SHG efficiency. The SHG efficiency from dark modes, which radiate under oblique incidence, is mainly determined by local field enhancement and far-field radiation efficiency. Although the nonlocal mode exhibits a higher $Q$ factor, it does not yield the strongest SHG response. Instead, the optimal SHG conversion efficiency arises in the local mode, attributed to stronger local field confinement and more effective out-of-plane radiation extraction. Our results reveal a different route toward high-efficiency nonlinear metasurfaces and offer opportunities for low-power, ultracompact photonic devices.

Recent experiments have reported nonlinear signals in topological materials up to room temperature. Here we show that this response stems from extrinsic spin-orbit contributions to both impurity and phonon scattering. While skew scattering dominates at low temperatures, the side jump contribution $\propto \tau /{\tau }_{\beta }$, where $\tau , {\tau }_{\beta }$ are the momentum and skew scattering times, respectively. Consequently side jump exhibits a weak temperature dependence and remains sizable at room temperature. Our results provide a roadmap for engineering nonlinear transport at ambient conditions.

Dynamical quantum phase transitions (DQPTs) are nonequilibrium transitions characterized by the orthogonality between an initial quantum state and its time-evolved counterpart following a sudden quench. Recently, studies of this phenomenon have been extended beyond closed quantum systems to include environmental interactions, often modeled through non-Hermitian effects. However, because non-Hermitian descriptions neglect both quantum jump processes and interaction effects, the ultimate fate of interacting quantum systems under full open-system quantum dynamics remains an open question. In this Letter, by incorporating both interactions and full Liouvillian dynamics, we prove that DQPTs in open quantum systems remain robust when subject to either particle loss or particle gain alone, but are generically smeared out when both processes coexist, as a result of many-body particle backflow. Furthermore, we uncover a nonperturbative dynamical effect: even a weak admixture of gain (loss) into a system with loss (gain) can dramatically reshape the long-time behavior of DQPT dynamics, leading to substantial deviations over time. These phenomena—including the universal smearing of DQPTs and the emergence of large dynamical deviations in the long-time limit—arise intrinsically from nonequilibrium many-body effects in open quantum systems. Our findings are general and substantiated by both analytical arguments and numerical simulations.

Due to the forming of low-energy flat bands, the moiré superlattices of the transition metal dichalcogenides are fascinating platforms for studying novel correlated states when such flat bands are fractionally filled, with the Coulomb interaction dominating. Here, we demonstrate that pressure can efficiently tune the flatness and quantum geometry of the single-particle bands in twisted bilayer ${\mathrm{MoTe}}_2$ ($t{\mathrm{MoTe}}_2$). By fractionally filling the topmost valence band, we find that pressure can act as a flexible means to modulate the fractional Chern insulator (FCI) and the generalized Wigner crystal (GWC) and control their many-body topological phase transitions. Moreover, our results indicate a remarkable correspondence between the single-particle band geometry and the formation of FCI and GWC. As the recent experiments report the presence of FCI phases in $t{\mathrm{MoTe}}_2$, our predictions could be readily implemented experimentally.

Entropy is an effective means to stabilize the high-temperature phase of a material. However, the origin of entropy is diverse, including configurational, vibrational, electronic, and magnetic, amongst others. It is still unclear, and sometimes controversial, which type of entropy plays a dominant role in a phase transition. Here, the individual entropy contributions during a hexagonal-close-packed (hcp) to face-centered-cubic (fcc) phase transition were quantified in transition metal based random solid solution alloys. We show, by inelastic neutron scattering measurements, that the vibrational entropy accounts for $\sim 80\%$ of the overall entropy change in a $\mathrm{C}{\mathrm{o}}_{75}\mathrm{N}{\mathrm{i}}_{25}$ binary alloy, whereas the contributions from electronic and magnetic entropy are small. First-principles calculations further identified that the excess vibrational entropy stems from the disappearance of optical phonon modes in the hcp phase. Analysis of a multicomponent $\mathrm{C}{\mathrm{r}}_{20}\mathrm{M}{\mathrm{n}}_{20}\mathrm{F}{\mathrm{e}}_{20}\mathrm{C}{\mathrm{o}}_{40}$ high-entropy alloy leads to the same conclusion, confirming the essential role of the vibrational entropy in driving the hcp-to-fcc phase transition in these alloys.

The sound velocity, melting curve, and phase diagram of ammonia have been investigated from 15 to 55 GPa and up to 3300 K using Brillouin spectroscopy of ${\mathrm{CO}}_2$ laser-heated ammonia samples in a diamond anvil cell. The melting transition was unambiguously identified from the appearance of the Brillouin peaks of fluid ammonia upon temperature increase, the latter being well resolved from that of the solid phase. Our melting temperatures are in good agreement with previous measurements and theoretical predictions. Within experimental uncertainties, we do not observe any discontinuous variation of the sound velocity or of the slope of the melting curve at the passage from plastic phase III to the superionic (SI) phase $\alpha$-SI, which is consistent with most previous experimental and theoretical results. We also find no evidence of the superionic $\gamma$-SI phase with fluidlike elastic behavior reported in a recent work and suggest that it was mistaken with the fluid phase.

${\mathrm{ZrTe}}_3$ is a prototypical quasi-one-dimensional compound undergoing a charge density wave (CDW) transition via a very sharp Kohn anomaly in phonon momentum space. While Fermi surface geometry has long been considered the primary driver of the instability, a full understanding of the lattice dynamics and electron-phonon role has remained elusive. Our first-principles calculations in the high-symmetry phase show that the Fermi surface is correctly reproduced only when the Hubbard interaction on the Te $5p$ orbitals is included, which in turn is essential for the appearance of a soft harmonic phonon mode at the CDW wave vector. Analyzing the mode and momentum dependence of the electron-phonon coupling, we find that its variations with phonon momentum dominate over electronic effects. These results identify unambiguously the CDW origin in ${\mathrm{ZrTe}}_3$ as a cooperative effect of Fermi surface geometry and momentum-dependent electron-phonon coupling, with the latter playing the leading role. We further determine the atomic structure in the low-symmetry CDW phase, revealing a nonchiral modulation. The mechanisms revealed in our work are directly relevant to other quasi-1D systems, including trichalcogenides and compounds hosting Peierls-like chains.

A regular lattice of magnetic skyrmions is the ground state of thin ferromagnetic films with Dzyaloshinskii-Moriya interaction in a relatively wide range of external magnetic fields. It was previously theoretically shown that upon the increase of magnetic field a topological transition in the magnon spectrum of such a skyrmion crystal (SkX) may occur. A nonuniform magnetic field may lead to localized magnon states emerging at the interface between two half planes of SkX. Using semiclassical quantization and the stereographic projection approach, we study such appearing edge states both in a full band structure calculation and in a simplified effective model. The latter effective model, described by an extended Dirac equation, is applicable to two relevant magnon bands near the $\mathrm{\Gamma }$ point. We show that both the chirality of emerging edge states and the degree of its localization at the interface are controlled by the magnetic field profile. We demonstrate that the localization length may be as small as a few interskyrmion distances.

The prediction of superconductivity above 200 K in ${\mathrm{CaH}}_6$ revolutionized research on hydrogen-rich superconductors, and subsequent experiments have verified this prediction, while unidentified peaks in x-ray diffraction and the decrease in superconducting temperature upon decompression indicate that unresolved issues remain. In this work, we reconstructed the accurate temperature-pressure phase diagram of the Ca-H system and determined the stability ranges of its candidate superconducting phases by considering anharmonic effects. Our results demonstrate that type-I clathrate ${\mathrm{Ca}}_8{\mathrm{H}}_{46-\delta }$ structures become thermodynamically stable at 0 K when anharmonic effects are considered. Notably, we found that the previously predicted ${\mathrm{CaH}}_6$ phase achieves stability above 500 K, underscoring the significant role of temperature and anharmonic effects in stabilizing this high-pressure phase. Our findings offer insights into the structure and superconducting mechanisms of hydrides.

Clathrate borides have attracted great interest owing to their cagelike boron frameworks with notable properties, including oxidation resistance, exceptional hardness, and superconductivity. Here, we systematically explore the Li-Y-B system across the pressure range of 0–100 GPa through extensive computational structure searches. ${\mathrm{LiYB}}_{12}$ and ${\mathrm{Li}}_2{\mathrm{YB}}_{12}$, forming a unique class of clathrate borides, are predicted to be thermodynamically stable at 5 and 28 GPa, respectively. Both structures comprise ${\mathrm{B}}_{12}$ and ${\mathrm{B}}_{24}$ cages that encapsulate Li and Y atoms, respectively, corresponding to Li-doped ${\mathrm{YB}}_{12}$. Further, electron-phonon coupling computational simulations predict superconducting critical temperatures of $\sim 1\mathrm{K}$ for ${\mathrm{LiYB}}_{12}$ and $\sim 2\mathrm{K}$ for ${\mathrm{Li}}_2{\mathrm{YB}}_{12}$ at 50 GPa, whereas they increase to $\sim 2$ and $\sim 6\mathrm{K}$ at 0 GPa, respectively. In addition, both ${\mathrm{LiYB}}_{12}$ and ${\mathrm{Li}}_2{\mathrm{YB}}_{12}$ are superhard materials with Vickers hardness $\ge 40$ GPa, comparable to that of ${\mathrm{YB}}_{12}$. These findings enrich the chemistry of boron clathrates and suggest a general strategy for designing lightweight superhard superconductors via electron doping of rigid boron-cage frameworks.

Motivated by exploring correlated metals with frustrating bond-dependent exchange interactions, we study hole- and electron-doped Kitaev Mott insulators on the triangular lattice. Using homogeneous parton mean-field theory, we find that the stripe antiferromagnetic (AFM) order for Kitaev coupling $K>0$ and the ferromagnetic (FM) order for $K<0$, both vanish at sufficiently large doping, beyond which we find regimes with chiral $d\pm id$ singlet pairing and $p\pm ip$ triplet pairing, respectively. Our tensor network computations, however, reveal that the superconducting correlations are strongly suppressed; while FM order stubbornly persists for the doped $K<0$ model, the doped $K>0$ model features emergent spin-charge modulated stripe orders. At higher hole doping for $K>0$, where AFM order is more strongly suppressed than for the electron-doped case, incorporating a sufficiently strong nearest-neighbor attraction yields evidence for singlet $d$-wave superconductivity with Luttinger parameter $K_{\mathrm{sc}}<1$. Our work sets the stage for a broader exploration of doping effects in triangular lattice magnets such as ${\mathrm{NaRuO}}_2$ that feature bond-dependent exchange interactions.