The long-standing question of whether the residual entropy of hexagonal ice ($S_h$) equals that of cubic ice ($S_c$) remains unresolved despite decades of research on ice-type models. While analytical studies have established the inequality $S_h\ge S_c$, numerical investigations suggest that the two values are very close. In this work, we revisit this problem using high-precision tensor network methods. In the Monte Carlo approaches used most commonly, the residual entropy cannot be directly obtained by sampling the ground-state degeneracy space. However, the tensor network framework enables an explicit encoding of the “ice rule” into local tensors, and then the residual entropy is transformed into finding the largest eigenvalue of a transfer operator in the form of a projected entangled-pair operator, which allows high-accuracy numerical evaluation. Meanwhile, we propose a perspective based on analyzing the normality of the transfer operator and examine it numerically with variational tensor network methods. This analysis allows for a direct computation for both residual entropies with our recently developed split corner transfer matrix renormalization group algorithm, providing a numerical evidence supporting the equality between $S_h$ and $S_c$.

Magnetic skyrmions driven by spin-orbit torque (SOT) are promising for energy-efficient spintronics. However, their description relies on dynamical models treating dissipation phenomenologically, leaving the fundamental dynamics-dissipation link unresolved. Here, we establish a thermodynamic framework bridging atomic spin dynamics with macroscopic thermodynamics. By decomposing SOT into conservative and nonconservative components, we complete the energy pathway from microscopic current injection to macroscopic heat, thereby transforming the observed velocity-dissipation decoupling from a phenomenological rule into a design principle governed by material parameters ($\beta {\gamma }_S$). As an energy-accounting framework for driven magnetic textures, it provides a quantitative route to connect transport with dissipation and heating, and it may be adapted to other driven ferroic textures when a Langevin-type description is applicable.

Here, we report the structure-property relationship in pressurized $4\mathit{Ha}-{\mathrm{TaSe}}_2$ single crystals. Electrical transport and low-temperature Raman spectroscopy measurements indicate a charge density wave (CDW) transition at $T_{\mathrm{CDW}}\sim 120$ K under ambient pressure. High-pressure transport experiments reveal a competitive relationship between superconductivity (SC) and CDW in $4\mathit{Ha}-{\mathrm{TaSe}}_2$. Under compression, the CDW order is progressively suppressed and vanishes abruptly at a critical pressure $P_{\mathrm{c}}$ of ∼19 GPa. In contrast, the superconducting transition temperature is gradually enhanced from $T_{\mathrm{c}}\sim 3.1$ K at ambient pressure to an optimal $T_{\mathrm{c}}\sim 7.8$ K at $P_{\mathrm{c}}$, followed by a slow reduction up to 83.7 GPa. Synchrotron x-ray diffraction experiments show that the pristine hexagonal structure remains stable under pressure, while the dimensionality transforms from quasi-2D to quasi-3D near $P_{\mathrm{c}}$. Simultaneously, Raman vibrational modes exhibit significant anomalies around $P_{\mathrm{c}}$, including changes in Raman intensity and pressure coefficients of normal in-plane modes, as well as in a two-phonon mode. Thus, the collapse of the CDW near $P_{\mathrm{c}}$ and the domelike superconducting phase diagram could be related to a dimensional crossover in the crystal structure. These findings not only establish the pressure-temperature phase diagram of $4\mathit{Ha}-{\mathrm{TaSe}}_2$ polytype but also facilitate the systematic understanding of the interplay between SC and CDW across the transition-metal dichalcogenides family of materials.

We perform first-principles electron-phonon calculations to evaluate the superconducting transition temperature $T_c$ for ternary superhard metals ${\mathrm{B}}_2{\mathrm{C}}_3\mathrm{N}$ and ${\mathrm{B}}_4{\mathrm{C}}_5{\mathrm{N}}_3$. An ambient-pressure $T_c$ of $\sim 40\mathrm{K}$ and $\sim 20\mathrm{K}$ is obtained respectively for ${\mathrm{B}}_2{\mathrm{C}}_3\mathrm{N}$ and ${\mathrm{B}}_4{\mathrm{C}}_5{\mathrm{N}}_3$ from the Eliashberg gap equations. The relatively high $T_c$ of these compounds is due in part to their high Debye temperatures associated with superhardness. The materials under study are potentially synthesizable, as their formation energies are comparable to those of other recently synthesized superhard B-C-N compounds. Therefore, studying superhard metals could hold the promise of realizing new higher-$T_c$ superconductors at ambient pressure.

The interplay of topology, disorder, and non-Hermiticity gives rise to phenomena beyond the conventional classification of quantum phases. We propose a one-dimensional non-Hermitian Su-Schrieffer-Heeger model with quasiperiodically modulated nonreciprocal intracell hopping. We show that quasiperiodic modulation can substantially enhance the topological regime and, remarkably, induce a non-Hermitian topological Anderson insulator (TAI) phase. Beyond the topological transition, increasing nonreciprocity drives a cascade of localization transitions in which all bulk eigenstates evolve from extended to multifractal critical and ultimately to localized states. Strikingly, the extended-to-critical transition coincides exactly with a real-complex spectral transition. We establish complete phase diagrams and derive exact analytical boundaries for both topological and localization transitions, uncovering an unanticipated coexistence of TAI and multifractal critical phases. Finally, we propose a feasible implementation in topolectrical circuits. Our results reveal a new paradigm for studying the cooperative effects of topology, quasiperiodicity, and non-Hermiticity.

This work examines a mobile impurity interacting with a bath of a few spin-$\uparrow$ and spin-$\downarrow$ fermions in a small one-dimensional open lattice system. We study ground-state properties using the exact diagonalization method, where the system is modeled by a three-component Fermi Hubbard Hamiltonian. We find that in addition to the standard phase separation between a strongly repulsive impurity and the bath, a strongly attractive impurity also phase separates with the fermionic holes due to the particle-hole symmetry. Furthermore, we find that the impurity can show an oscillatory pattern in its density for intermediate attractive and repulsive bath-impurity interactions, which are induced by Friedel oscillations in the finite-size fermionic bath. This rich behavior of the impurity could be probed with fermionic ultracold mixtures in optical lattices.

The physical origin of third harmonic magnetoresistance remains debated in nonlinear spintronics. Here we systematically study third harmonic magnetoresistance in Ni-based films with different in-plane anisotropies, including polycrystalline Ni and epitaxial Ni(001) systems. Using in-plane field-rotation measurements together with magnetic-field scaling, we identify thermal anisotropy modulation as a dominant mechanism, distinct from the conventional thermal magnetization modulation. ac Joule heating induces periodic temperature oscillations that modulate magnetic anisotropy constants, driving coherent magnetization oscillations. This mechanism produces distinct angular fingerprints, such as a characteristic sixfold symmetry in Ni(001) films with fourfold magnetic anisotropy. By establishing a quantitative framework based on the $1/H$ and $1/H^2$ scaling relations, we effectively decouple the thermal contributions arising from current-induced modulations of uniaxial and fourfold magnetic anisotropies. Our findings provide a rigorous methodology for interpreting higher-order harmonic transport and highlight thermal-anisotropy coupling as an essential ingredient in nonlinear spintronic measurements.

The finite mass of a skyrmion in a ferrimagnet, which is determined by the exchange interaction between spins belonging to different ferrimagnetic sublattices, leads to a gyroscopic motion of skyrmions, which is conceptually similar to the electron cyclotron resonance (ECR) in metals. We show that it can be excited in a ferrimagnetic film by a spin current or microwaves. Similar to how the ECR permits measurement of the effective electron mass, the skyrmion cyclotron resonance (SCR) must permit unambiguous measurement of the skyrmion mass. The presence of massive skyrmions strongly influences the spectrum of spin excitations in a ferrimagnet. The dependence of the SCR frequency on parameters is computed for a TM/RE (transition-metal/rare-earth) ferrimagnet, using CoGd as an example. The cyclotron frequency exhibits a dip near angular momentum compensation, where it hybridizes with the ferromagnetic resonance. The skyrmion cyclotron mode is studied for individual skyrmions and for skyrmion lattices, where the effect must be strong enough to be observed in microwave and spin-current experiments.

We develop a unified theory of nonadiabatic wave-packet dynamics for Bloch electrons subject to slowly varying spatial and temporal perturbations. Extending the conventional wave-packet ansatz to include interband contributions, we derive the equation governing the interband coefficients from the time-dependent variational principle and refer to it as the wave-packet coefficient equation. Near the adiabatic regime, we can integrate out the small interband amplitudes to obtain the leading nonadiabatic corrections to the effective wave-packet Lagrangian. These corrections take three forms: (i) a nonadiabatic metric in real and momentum space, which in two-band models reduces to an energy-gap-renormalized quantum metric; (ii) gauge-invariant corrections to the Berry connections governing the motion of the wave-packet center; and (iii) an energy correction induced by spatial and temporal variations of the Hamiltonian. When the nonadiabatic metric is invertible, the dynamics can be recast as forced geodesic motion in phase space, providing a restricted gravitational analogy for Bloch-electron dynamics. As an illustration, we apply the formalism to one-dimensional Dirac electrons coupled to a slowly varying exchange field.

The existence of an elementary magnetic pole (charge) was predicted by Dirac in 1931 and here we propose and implement semiconductor nanostructures supporting such poles, which are InN/GaN heterostructure nanowires (NWs) with a few monolayer thick InN inclusions, grown using plasma-assisted molecular beam epitaxy. The formation of magnetic pole/charge occurs in this NWs due to piezoelectric effect leading to formation of Wigner quantum dots (WQDs) having magnetoelectron states—Dirac anyons (DAs), created by magnetic flux quanta self-generated in single-particle states, previously observed in self-assembled InP/${\mathrm{GaInP}}_2$ WQDs [Mintairov et al., Phys. Rev. B 111, 045410 (2025)]. The formation of WQDs and DAs/magnetic poles having intrinsic magnetic field of several tens of Tesla is evident from the multipeak structure and up to 100% of circular polarization degree of the photoluminescence spectra measured for single NWs. This is supported by the calculations of single-particle states using $\overline{k}·\overline{p}$ model and electron density distributions using the configurational interaction approach. The presented results demonstrate the scaling of magnetic pole/Dirac anyon properties with material parameters, which allows the realization of high-temperature magnetic pole structures that can be used in nanophotonics and topological quantum computing applications.

We investigate the optical properties of neutral excitons in CdTe/ZnTe quantum dots containing a single ${\mathrm{Ni}}^{2+}$ ion. We show that the photoluminescence spectra provide a direct spectroscopic signature of strain-induced mixing of the ${\mathrm{Ni}}^{2+}$ spin states. A misalignment between the principal axis of the local strain tensor and the quantum dot growth direction reorients the spin quantization axis of the magnetic ion, reducing the $\mathrm{hole}\text{−}{\mathrm{Ni}}^{2+}$ exchange interaction at low magnetic field and giving rise to photoluminescence replicas around the partially linearly polarized bright-exciton transitions. A longitudinal magnetic field restores the circularly polarized optical selection rules, allowing the three spin projections $S_z=0,\pm 1$ of the ${\mathrm{Ni}}^{2+}$ ion to be spectrally resolved. Dark-exciton emission appears on the low-energy side of the spectra and is dominated at low field by transitions involving spin flips of the magnetic ion. An effective spin Hamiltonian including strain orientation and valence-band mixing reproduces the magnetic-field evolution of both bright- and dark-exciton spectra. These results highlight the key role of the local strain environment in determining the spin-exciton coupling of transition-metal dopants in semiconductor quantum dots.

The work functions of ${}^7\mathrm{Li}$ and ${}^6\mathrm{Li}$ metals have been measured as a function of temperature, by using photoionization of pure isolated metal nanoparticles in a beam. These data reveal a marked isotope effect in the temperature variation of these work functions. Furthermore, for both isotopes the curvature of this temperature variation is found to be significantly larger than may be ascribed purely to a change in the electron-gas density. These findings enhance the characterization of lithium as a quantum material in which the interplay between electronic and ionic degrees of freedom is nontrivial, and call for a microscopic understanding beyond simple models. Additionally, the slope of the work-function curves was observed to vanish in the low-temperature limit, as had been predicted on the basis of the Third Law of Thermodynamics.

We report an advanced formulation of the Fourier modal method developed for two-dimensionally periodic multilayered structures containing materials with nonzero macroscopic magnetoelectric coefficients (also known as coefficients of chirality and bianisotropy) represented as arbitrary $3\times 3$ tensors. We consider two numerical schemes for this formulation: with and without generalized Fourier factorization rules. For both schemes, we provide explicit expressions for the Fourier tensors of macroscopic material parameters and demonstrate that, in the absence of magnetoelectric coupling, they reduce to the conventional factorization rules. We show that the scheme employing factorization rules facilitates improved convergence, even when the macroscopic chirality coefficient is large. The described formulation represents a fast and rigorous technique for theoretical studies of periodic structures with chiral, bianisotropic, or nonreciprocal materials in the widely used framework of the Fourier modal method.

Two-dimensional Janus materials, characterized by their inherent structural asymmetry, provide an ideal platform for coupling magnetism with valleytronic properties. Herein, we propose two hydrogenated Janus monolayers, GdISeH and GdITeH, based on experimental layered ${\mathrm{GdI}}_2$, which leverage the strong spin-orbit coupling of gadolinium. Their structural, magnetic, electronic, and valleytronic properties are systematically investigated using first-principles calculations, Monte Carlo simulations, and Wannier function analysis. Both monolayers exhibit a ferromagnetic ground state with in-plane magnetic anisotropy (IMA) and high Curie temperatures of 216 K for GdISeH and 190 K for GdITeH. When magnetized out of plane, they exhibit substantial valley polarization (163 meV for GdISeH and 196 meV for GdITeH) along with prominent valley-contrasting Berry curvature, satisfying the key requirements for the anomalous valley Hall effect (AVHE). The electronic states are highly tunable: biaxial strain drives phase transitions among bipolar magnetic semiconductor (BMSC), bipolar magnetic semimetal (BMSM), and unipolar magnetic semiconductor (UMSC) phases, while carrier doping induces switching between BMSC and half-metal (HM) states. Notably, a low concentration of hole doping (below approximately 0.02 $h$/f.u. for GdISeH and slightly above this for GdITeH) switches the magnetic anisotropy from IMA to perpendicular magnetic anisotropy, which is essential for stabilizing valley polarization and realizing the AVHE. The high-temperature ferromagnetism, large valley polarization, AVHE, as well as versatile BMSC, BMSM, UMSC, and HM characteristics with high spin polarization make Janus GdISeH and GdITeH monolayers promising candidates for spintronic and valleytronic applications.

We consider a half-filled two-dimensional Su-Schrieffer-Heeger lattice and examine the role of the long-range Coulomb electron-hole attractive interaction. We demonstrate that under specific conditions, a rare interplay of topological and excitonic-collective behavior emerges as a novel state of matter. A unique Bose-Einstein condensate of excitons forms, exhibiting the co-presence of pseudospin chiral texture. The emerging complex order parameter, a particle-hole pairing gap, has nonzero real and imaginary parts throughout the Brillouin zone (BZ) but vanish separately on two different nodal lines, which intersect at two Weyl points. The Weyl nodes possess opposite pseudospin chiralities, which act as source and drain of a Berry flux associated with the particle-hole pairing wave function, and are the cause of Bogoliubov–de Gennes Fermi-arc edge states. We self-consistently calculate the full momentum dependence of the particle-hole pairing gap throughout the entire BZ. Near the Weyl points, the pairing gap exhibits the unconventional $p_x+i{p}_y$ character. Finally, we discuss general potential experimental realizations of this novel state of matter.

Multiexciton states in monolayer transition metal dichalcogenides represent fertile ground for uncovering emergent many-body quantum behaviors, particularly in the context of valley polarization and coherence. Understanding how complex excitonic correlations influence valley-resolved optical properties is essential for both fundamental valleytronic science and potential quantum applications. Here, we investigate the valley-selective polarization characteristics of hexcitons—six-body bound states—in monolayer ${\mathrm{WSe}}_2$. Surprisingly, we observe that hexciton photoluminescence exhibits strong circular polarization but negligible linear polarization, indicating that valley polarization is well preserved, while valley coherence is entirely lost. This decoupling behavior stands in stark contrast to neutral excitons, which typically exhibit both forms of polarization, and points to fundamentally different valley dynamics in higher-order excitonic complexes. Our analysis reveals that, despite nominally symmetric excitation and emission configurations at the +$K$ and $-K$ valleys, the exchange interactions and spins in the many-body final states subtly break the conditions required for intervalley coherence, suppressing any linear polarization signature. These findings shed light on the intrinsic decoherence mechanisms in multiexciton systems and highlight the critical role of many-body effects in shaping the valley quantum dynamics of two-dimensional semiconductors.

The transition from order to disorder is conventionally regarded as detrimental to solid-state heat transfer in classical wave and quasiparticle systems. In striking contrast, we show that in near-field thermal radiation, breaking long-range order—shifting from periodic to quasiperiodic configurations—induces a counterintuitive enhancement of energy transport. When the transmission structure transitions from a conventional periodic photonic crystal to a quasiperiodic Fibonacci geometry, the radiative heat flux can increase by more than an order of magnitude. This effect arises from delocalized interactions within quasiperiodic elements, where quasiperiodicity relays and amplifies thermal electromagnetic energy transfer across large spatial separations, surpassing even corresponding near-field scenarios. The extraordinary transport properties induced by quasidisorder in near-field thermal radiation could open possibilities for heat-flow manipulation, offering transformative implications for thermal science and advancing the fundamental understanding of collective excitations in non-ordered systems.

Altermagnets are a recently discovered class of compensated magnets with momentum-dependent spin splittings and unusual transport properties, even without a net magnetization. In the presence of combined fourfold rotation and time-reversal ($C_4\mathcal{T}$) symmetry, linear and also second order, driven by a Berry curvature dipole, anomalous Hall responses are forbidden in any pure $d$-wave altermagnet. Nevertheless, here we find that the nontrivial quantum metric of the occupied Bloch states allows for an electric field induced Berry curvature dipole, which generates a strong and tunable second-order Hall current, enabling it to be switched on or off by simply adjusting the relative orientation between the symmetry-reducing dc field and the ac probe field. Specifically, we investigate the electric field induced second-order anomalous Hall response in a two-dimensional Rashba-coupled altermagnet with varying $d_{x^2-y^2}$ ($B_{1g}$) and $d_{xy}$ ($B_{2g}$) altermagnet symmetry to capture all possibilities. Crucially, the nonlinear signal is highly sensitive to the underlying symmetry of the altermagnetic order at specific doping levels, offering a purely electrical method to distinguish distinct altermagnetic orders. Our results position altermagnets as a promising platform for controllable nonlinear transport and spintronic applications.

We determine the magnetic ground state of the kagome lattice magnet ${\mathrm{Nd}}_3{\mathrm{Ru}}_4{\mathrm{Al}}_{12}$ by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet (“hex-FM”) with uniform moment length and ordering vector $\mathit{Q}=0$, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, here called the “ortho-FM” state. Our analysis of the flipping ratio in polarized neutron scattering is consistent with the hex-FM state. The results provide a microscopic basis for understanding the large fluctuation-induced Hall and Nernst responses near $T_{\mathrm{C}}\approx 41\mathrm{K}$, as previously reported for ${\mathrm{Nd}}_3{\mathrm{Ru}}_4{\mathrm{Al}}_{12}$.