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.

Halide perovskites have emerged in the past decade as a new important class of semiconductors for a variety of optoelectronic applications. A lot of previous studies were thus devoted to the characterization of their point defects. Positron annihilation spectroscopy is a well recognized tool for probing vacancies in materials. Recent applications of this technique to ${\mathrm{APbX}}_3$ halide perovskites are sparse and the rare theoretical predictions of positron lifetimes in these materials, published in association with experiments, do not fully agree with each other. These works suggest that vacancies on the $A$ site are not detected. In our theoretical study we focus on the role of the electron-positron correlation functional. We thoroughly revisit and compare several approximations when applied to methylammonium lead iodide (${\mathrm{MAPbI}}_3$) with or without vacancies, as well as inorganic perovskites ${\mathrm{CsPbI}}_3$ and ${\mathrm{CsPbBr}}_3$, in various phases. We show also the relationship between the size of the voids, through Voronoi volumes, and the calculated lifetimes. For the cubic phases we investigate in detail the role of polymorphism, including the distribution of vacancy formation energies and positron annihilation lifetimes. In our lifetimes calculations, apart from older and more recent semilocal approximations for the electron-positron correlation potential, we also consider the weighted density approximation, which is truly nonlocal and should better describe positron annihilation in regions with strong electronic density variations. We show that for this class of materials, and especially for cations vacancies, the influence of the chosen approximation is crucial, much stronger than in metals, alloys, and conventional semiconductors. This influence may induce one to reconsider the interpretation of experimentally determined lifetimes.

The contribution of extrinsic skew scattering to the anomalous Nernst effect (ANE) provides a potential avenue to enhance transverse thermoelectric response through spin-dependent scattering mechanism. In this study, we show the effect of ${\mathrm{Cu}}_{95}{\mathrm{Ir}}_5$ addition on the enhancement of the anomalous Nernst thermopower $\left(S_{\mathrm{ANE}}\right)$ in a CoFe thin film. A high-throughput screening based on the lock-in-thermography method for thermal responses induced by the anomalous Ettingshausen effect (AEE), the reciprocal of ANE, across a composition-spread thin film of CoFe-${\mathrm{Cu}}_{95}{\mathrm{Ir}}_5$ identified the optimal composition for ANE. Based on this screening experiment, we fabricated the specific composition ${\left(\mathrm{CoFe}\right)}_{63}{\left({\mathrm{Cu}}_{95}{\mathrm{Ir}}_5\right)}_{37}$ film and measured the electric and thermoelectric transport properties. The $S_{\mathrm{ANE}}$ value reaches 1.23 µV/K for ${\left(\mathrm{CoFe}\right)}_{63}{\left({\mathrm{Cu}}_{95}{\mathrm{Ir}}_5\right)}_{37}$ at room temperature, which is much higher than that for CoFe as well as composition-matched references ${\left(\mathrm{CoFe}\right)}_{64.85}{\left(\mathrm{Cu}\right)}_{35.15}$ and ${\left(\mathrm{CoFe}\right)}_{98.15}{\left(\mathrm{Ir}\right)}_{1.85}$, which contain the same amount of only Cu and only Ir, respectively. The scaling analysis on the anomalous Hall effect reveals that the extrinsic skew-scattering contribution is significantly greater for the ${\left(\mathrm{CoFe}\right)}_{63}{\left({\mathrm{Cu}}_{95}{\mathrm{Ir}}_5\right)}_{37}$ film compared to others at 300 K. This enhancement in the extrinsic contribution is attributable to the cooperative role of Cu and Ir; Ir acts as a dominant source of skew scattering due to large spin-orbit interaction, while Cu modifies the scattering potential symmetry and accelerates the skew scattering. These results offer an effective strategy for boosting $S_{\mathrm{ANE}}$ and provide critical insights into extrinsic mechanisms for ANE.

Noncentrosymmetric crystal structures are of significant interest due to the peculiar physical phenomena they frequently promote. Among mercury-based compounds, only a few noncentrosymmetric materials are known, with the vast majority remaining unexplored. In this work, we examine the family of noncentrosymmetric mercurides ${\mathrm{Na}}_{11}{\mathrm{Hg}}_{52}$ and $A_{11-x}{\mathrm{Hg}}_{54+x}$ ($A$ = Ca or Sr). All three materials are identified as new superconductors. The values of the critical temperatures are fairly modest, ranging from 1.7 K (${\mathrm{Ca}}_{11-x}{\mathrm{Hg}}_{54+x}$) to 3.1 K (${\mathrm{Na}}_{11}{\mathrm{Hg}}_{52}$). We postulate that the superconductivity of noncentrosymmetric ${\mathrm{Na}}_{11}{\mathrm{Hg}}_{52}$ and $A_{11-x}{\mathrm{Hg}}_{54+x}$ ($A$ = Ca or Sr) compounds is likely conventional.

We investigate the stabilization of topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with a specific emphasis on the intraband FFLO phase, in a one-dimensional Fermi gas subjected to an external magnetic field. This research highlights the crucial role of the interplay between Rashba spin-orbit coupling (RSOC) and Dresselhaus spin-orbit coupling (DSOC). Employing a Fermi-Hubbard model alongside the density matrix renormalization group (DMRG) method, we examine the combined effects of RSOC and DSOC on these exotic superfluid phases, taking into account attractive fermionic interactions. Our principal finding reveals that while RSOC primarily stabilizes conventional zero-momentum pairing, DSOC performs a distinct and crucial role in selectively stabilizing the intraband FFLO phase. This stabilization is achieved by enhancing spin polarization within a single helicity band and suppressing interband coherence, thereby facilitating the formation of finite-momentum FFLO pairs within the same band and resulting in the emergence of a topologically nontrivial superfluid. This targeted control of intraband FFLO pairing paves the way for new strategies in the manipulation of superfluid phases in spin-orbit coupled systems and offers essential insights for experimental realizations in ultracold atomic gases, with implications for topological quantum computing and Majorana fermions.

There are multiple possible origins of transport anisotropies in metals and superconductors. For instance, rotational symmetry can be spontaneously broken in the normal state as a result of electronic nematic order inducing anisotropies in an otherwise $s$-wave superconducting state. Another possibility is that the dominant source of rotational symmetry breaking is the superconductor itself and its vestiges that may survive in the normal state. We here theoretically analyze the correlations of transport anisotropies in the normal and the corresponding superconducting phase for different scenarios of broken symmetry, either coming solely from the normal state, solely from the superconductor and its vestiges in the metallic regime, or simultaneously from both. We further include both zero-momentum and finite-momentum pairing; we develop a theory of vestigial order for the latter, characterized by broken rotational and translational symmetry. Our findings reveal that the relative transport anisotropies in the normal and superconducting phases sensitively depend on the scenario, including the form of vestigial order and, in some cases, the parity of the superconducting order parameter. As such, measuring the directional dependence of the critical current and resistivity can provide strong constraints on the origin of rotational symmetry breaking. We demonstrate our findings in minimal models relevant to twisted multilayer graphene, rhombohedral graphene, and twisted transition-metal dichalcogenides.