The motivation behind the present work is to adopt methodology from field theory and high-energy physics to crystallography. In particular, we establish a relationship between the electromagnetic sector of the standard-model extension (SME) for Lorentz invariance violation and optical media. At an effective level, a broad class of anisotropic and polarization-dependent electromagnetic properties associated with crystal structures is demonstrated to be parametrized in the SME. Crystallographic and magnetic point groups provide the mathematical tools to show this correspondence. Birefringent and magnetoelectric media merit separate studies. Intriguing effects, which have not been described systematically in the modern literature, are rediscovered for the latter and expressed in the SME language. With the setting developed at our disposal, materials with specific symmetries such as birefringent or multiferroic crystals serve as condensed-matter analogs of SME effects. It enables us to propose materials with unusual optical properties, which have not been thoroughly investigated in recent times.

We employ the flux-flow instability (FFI) technique—a widely used method for determining the quasiparticle relaxation time (${\tau }_E$)—to investigate single-crystal superconducting titanium nitride (TiN) films characterized by weak vortex pinning and slow electron-phonon relaxation. By systematically varying the TiN strip width, we show that reliable extraction of the vortex velocity and ${\tau }_E$ is achievable only when the strip width exceeds the electron-phonon relaxation length. A comparative analysis of ${\tau }_E$ values obtained using various FFI models and other experimental methods reveals that quasiparticle relaxation within the vortex core is primarily governed by an increase in quasiparticle temperature. Our analysis provides a reliable way to determine ${\tau }_E$ from FFI measurements and may also be relevant to other superconducting systems in which fast electron-electron scattering is expected to lead to a thermal-like quasiparticle distribution function.

The structural evolution and transformation pathways of carbon dioxide phase IV (${\mathrm{CO}}_2$-IV) are investigated over 13.0–76.7 GPa and 296–700 K using synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations. ${\mathrm{CO}}_2$-IV was obtained from ${\mathrm{CO}}_2$-I by isothermal compression to 13.0 GPa at 600 K. Subsequent single-crystal diffraction performed at 14.5 GPa and 296 K confirms that ${\mathrm{CO}}_2$-IV adopts a rhombohedral $\text{R}\overline{3}\text{c}$ structure, consistent with Datchi et al. [Phys. Rev. Lett. 103, 185701 (2009)], establishing its purely molecular character without evidence for an “intermediate bonding state”. At room temperature, deviatoric stress promotes a symmetry-lowering distortion of $R\overline{3}c$ ${\mathrm{CO}}_2$-IV at 14.6 GPa, yielding a distorted molecular configuration described by a triclinic $P1$ model, denoted here as an ${\mathrm{IV}}^{\prime }$-type distortion. From 296 to 600 K, the onset pressure of this distortion increases modestly, giving rise to a positively sloped kinetic onset line in the $P$–$T$ diagram. At 650 and 700 K, enhanced thermal relaxation substantially reduces the influence of deviatoric stress, and no symmetry breaking is detected before the molecular-to-nonmolecular transformation, stabilizing the $R\overline{3}c$ structure in the molecular regime. Upon further compression, the molecular solid transforms into metastable nonmolecular states containing mixed three- and fourfold-coordinated carbon atoms. The transformation pathway is temperature dependent: at 296–600 K, amorphization proceeds from the $P1$-distorted form of ${\mathrm{CO}}_2$-IV to a-${\mathrm{CO}}_2$, whereas at 650–700 K the transformation proceeds directly from $R\overline{3}c {\mathrm{CO}}_2$-IV to the more ordered metastable covalent phase VI. The onset pressure of the molecular-to-nonmolecular transformation decreases with increasing temperature. These results reveal that the high-pressure behavior of ${\mathrm{CO}}_2$ is governed by the interplay between deviatoric stress and thermal activation, which controls symmetry lowering within the molecular regime and the subsequent pathways toward amorphous and metastable covalent structures.

The current-driven resistive transition is central to superconducting single-photon detectors, transition-edge sensors, and fluxonic devices. Depending on sample uniformity, dimensions, and heat removal, it can be driven by phase-slip events, flux-flow instabilities (FFI), and normal-domain formation. Here we investigate the influence of two types of microstructural defects on vortex dynamics in ${\mathrm{MgB}}_2$ films: columnar growth in textured films and buffer-layer roughness in single-crystal films. The current-voltage ($I\text{−}V$) curves measured at $T\approx 0.25T_c$ for both films exhibit multiple steps. Time-dependent Ginzburg-Landau simulations reproduce the major features of the experimental $I\text{−}V$ curves and suggest that the resistive transitions for both films are mediated by the formation and growth of normal domains rather than FFI. The single-crystal film with buffer-layer roughness exhibits superconductivity breakdown at higher currents and pinning activation energies approximately twice those of the textured film, along with more pronounced multistep features in the $I\text{−}V$ curves. These features are primarily attributed to stronger pinning induced by lateral variations of the superconducting order parameter along the MgO buffer layer. Our results show that both the film microstructure and the film-buffer interface are critical for the resistive transition, offering insights for superconducting devices requiring controlled dissipation at high transport currents.

In spintronics, both electronic charge and spin are used to process and store information. The generation, manipulation, and detection of spin currents are essential for the development of next-generation spintronic technologies. Here, we investigate the spin Hall effect in electronic Lévy glasses composed of graphene ribbons with randomly distributed circular regions of high spin-orbit coupling. These systems exhibit two transport regimes that can be tuned by adjusting the Fermi energy. The superdiffusive regime is characterized by low Fermi energy, low resistivity, and low magnetoresistivity, resulting in a long spin diffusion length, in contrast to the diffusive regime. Employing the Landauer-Büttiker approach in conjunction with numerically exact tight-binding simulations, we compute spin-resolved transmission coefficients to assess the spin Hall current and the spin Hall angle as functions of Fermi energy, spin-orbit coupling strength, and on-site electrostatic potential. Our findings reveal that, in the superdiffusive regime, a low charge current can be converted into a large spin Hall current, whereas in the diffusive regime, the same charge current generates a modest spin Hall current. Moreover, we observe that the spin Hall angle can reach 30% in the superdiffusive regime, whereas in the diffusive regime it is only 5%. These results demonstrate that electronic Lévy glasses provide a versatile platform for controlling spin transport and optimizing the spin Hall effect for spintronic applications.

Near-field radiative heat transfer can exceed the blackbody limit by orders of magnitude due to evanescent electromagnetic coupling across subwavelength gaps. While such enhancement has been widely studied in planar and nanostructured systems, the role of engineered meta-atoms in controlling near-field heat transfer remains largely unexplored. We found that the local arrangement of meta-atom pairs modifies the electromagnetic response and opens additional photon-tunneling channels, leading to a significant enhancement of thermal transport. In particular, near-field activated dark modes play a dominant role at small separations, while their rapid suppression at larger gaps results in a strong distance-dependent reduction in heat transfer. As a result, the total radiative thermal conductance can be enhanced by up to 7 orders of magnitude compared to a planar reference, with an additional enhancement factor of up to 32 achieved by varying the intrapair configuration of the meta-atoms at a separation of 2 $\mu \mathrm{m}$. These findings establish the light-matter interaction as a powerful degree of freedom for controlling near-field thermal radiation.

Titanium diboride (${\mathrm{TiB}}_2$) is a representative ultrahigh-temperature ceramic and topological semimetal with exceptional mechanical and thermal properties. However, a comprehensive understanding of its intrinsic thermal transport mechanisms remains lacking. Here, we present a systematic first-principles investigation of the coupled electron and phonon thermal transport in ${\mathrm{TiB}}_2$. We find that strong phonon-electron scattering suppresses the phonon thermal conductivity by nearly a factor of 5 even at room temperature, resulting in an unusually weak temperature ($T$) dependence rather than the conventional $T^{-1}$ behavior. In contrast to common metals, the electronic thermal conductivity increases monotonically even in the high-temperature regime, driven by the anomalous energy dependence of the carrier lifetime associated with a pronounced dip in the electronic density of states near the Fermi level. Moreover, the symmetry-protected topological band crossings near the Fermi energy promote substantial electron-hole compensation, which enhances the electronic thermal conductivity and drives the Lorenz number above the Sommerfeld value. Our work establishes a unified picture of heat conduction in ${\mathrm{TiB}}_2$ and highlights the role of its topological multiband electronic structure in shaping anomalous thermal transport.

For charged particles, their orbital angular momentum (OAM) in solids has a direct magnetic manifestation as an orbital magnetization. For charge-neutral particles, however, the physical manifestation of the OAM in solids remains unclear. Here, we show that a charge-neutral particle carrying a magnetic moment couples to an electric-field gradient through the Aharonov-Casher (AC) effect, thereby exhibiting the electric quadrupole in crystalline solids. This AC-induced electric quadrupole (AC-EQ) contains the scalar, toroidal dipole, and reduced quadrupole components, which are conjugate to the divergence, circulation, and shear of the electric field, respectively. As representative examples, we calculate the AC-EQ of magnons in two magnetic systems. In ferromagnetic pyrochlore, Dzyaloshinskii-Moriya interaction (DMI) induces a sizable AC-EQ, whereas in helical $\mathrm{Fe}$ langasite the AC-EQ emerges from the helical spin configuration even in the absence of DMI.

We report the crystal structure and magnetic properties of a $S=\frac{3}{2}$ anisotropic triangular lattice compound ${\mathrm{Na}}_3\mathrm{Cr}$(${\mathrm{PO}}_4{)}_2$ employing single-crystal and powder x-ray diffraction, magnetization, heat capacity, and ${}^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) experiments, supported by band structure calculations. Magnetic susceptibility exhibits a broad maximum at around 3.5 K, indicating the presence of a short-range antiferromagnetic order, typical of a low-dimensional spin system. Magnetization and heat capacity manifest an antiferromagnetic long-range ordering at around $T_{\mathrm{N}}\simeq 2.6\mathrm{K}$. This was further confirmed by the drastic NMR line broadening and a peak in the nuclear spin-lattice and spin-spin relaxation rates. The isothermal magnetization data exhibit a field-induced transition at around ${\mu }_0{H}_{\mathrm{SF}}\simeq 1.7\mathrm{T}$ reminiscent of an anisotropic two-dimensional magnet, before saturating above ${\mu }_0{H}_{\mathrm{sat}}\simeq 4.5\mathrm{T}$. The saturation field was further upheld by the field-dependent NMR relaxation measurements at low temperatures. The ${}^{31}\mathrm{P}$ NMR spectral shape confirms the commensurate antiferromagnetic nature of the ordering below $T_{\mathrm{N}}$. Ab initio calculations reveal a significant deformation of the triangular spin lattice, resulting in triangles with two antiferromagnetic couplings of similar strength and a much weaker coupling along the third side of the triangle.

Altermagnets enable spin-split bands and anomalous transport phenomena with vanishing net magnetization, yet the symmetry-governed dependence of their optical and spin transport responses on the Néel-vector orientation remains largely unexplored. Using first-principles calculations and systematic magnetic point group analysis, we establish the complete response tensor forms dictated by the magnetic point group for the typical altermagnet CrSb, revealing a fundamental dichotomy: first-order Kerr/Faraday effects, governed by the antisymmetric optical conductivity, are odd functions of the Néel vector, while second-order Voigt/Schäfer-Hubert effects, determined by diagonal dielectric anisotropies, are even functions. Quantitatively, the Kerr rotation angle reaches up to $\sim 0.55\mathrm{mrad}$, the Faraday rotation up to $\sim 6.9\times {10}^5\mathrm{mrad}/\mathrm{cm}$, and the Voigt rotation up to $\sim {10}^6\mathrm{mrad}/\mathrm{cm}$, with their angular dependencies following distinct symmetry patterns. For the spin Hall effect, the time-reversal-odd ($\mathcal{T}$-odd) and time-reversal-even ($\mathcal{T}$-even) contributions to the spin Hall conductivity coexist and are of comparable magnitude ($\sim {10}^2\frac{\hslash }{e}\frac{\mathrm{S}}{\mathrm{cm}}$). In the ground-state Néel configuration along the $c$ axis, the $\mathcal{T}$-even spin Hall conductivity reaches $265\frac{\hslash }{e}\frac{\mathrm{S}}{\mathrm{cm}}$, while the $\mathcal{T}$-odd component is $85\frac{\hslash }{e}\frac{\mathrm{S}}{\mathrm{cm}}$, corresponding to charge-to-spin conversion efficiencies of 1.63% and 0.52%, respectively. Notably, reorienting the Néel vector not only modulates the transverse spin Hall components but also activates longitudinal spin-current–charge-current configurations (e.g., ${\sigma }_{xx}^{S_z}$ and ${\sigma }_{yy}^{S_z}$ for $\mathit{N}\left|\right|\frac{1}{2}\mathit{a}+\mathit{b}$), which are strictly forbidden in the conventional spin Hall effect. These results establish a comprehensive, symmetry-governed framework for the Néel-vector dependence of magneto-optical and spin-transport responses in CrSb, offering a multidimensional response spectrum for probing the Néel vector direction.

The results of a study of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Ge}(0\le x\le 0.3)$ compounds using nuclear magnetic resonance (NMR) spectroscopy on the nuclei of ${}^{57}\mathrm{Fe}$ and ${}^{59}\mathrm{Co}$ in helical spin ordered state are represented in this paper. It was established that cobalt atoms are randomly distributed within the crystal structure of ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Ge}$. The hyperfine fields and magnetic moments for iron and cobalt atoms were determined at a temperature of $T=4.2\mathrm{K}$. The average Fe magnetic moment decreases from 0.9 ${\mu }_{\mathrm{B}}$ (for $x=0$) to 0.85 ${\mu }_{\mathrm{B}}$ (for $x=0.3$), whereas the Co magnetic moment is of about zero. It is shown that the hyperfine fields induced at the Co nuclei by Fe atoms arise from the strong hybridization of the Fe $3d$ and Co $3d$ orbitals.

Spin-transfer torques provide a direct means of controlling magnetic equilibria, damping, oscillation frequencies, and non-Hermitian mode dynamics. However, when dampinglike and fieldlike torques act simultaneously, their distinct roles in the static and dynamical response are not readily apparent in the original Landau-Lifshitz-Gilbert (LLG) equation. Here we derive an affine tangent-plane linearization of the LLG equation with both torque components, which separates the inhomogeneous term responsible for the current-induced equilibrium displacement from the homogeneous non-Hermitian matrix governing local precession and stability. This formulation provides a transparent and directly testable separation of the static and dynamical roles of the two torque components. From the trace and determinant of the dynamical matrix, we show that for small-amplitude oscillations, the dampinglike torque predominantly controls the decay time, while the fieldlike torque shifts the effective restoring coefficients and therefore tunes the oscillation frequency. For the minimal angular torque form considered here, the transverse component of the spin polarization controls the leading static displacement, whereas the longitudinal component enters the homogeneous operator, controls the leading torque-induced corrections to the decay rate and oscillation frequency, and affects the displacement only at higher order. The stiffness matrix $K$ is identified as the conservative response kernel that maps spin-torque forces onto equilibrium magnetization shifts. The dampinglike and fieldlike torques generate orthogonal driving forces, but their induced displacements are generally nonorthogonal due to anisotropic stiffness. Finally, we analyze exceptional points (EPs) of the non-Hermitian linearized dynamics and show that the torque combinations $C_I$ and $C_J$ separately govern the stability of the coalesced mode and the eigenvalue-coalescence condition. Tuning one conservative tangent-plane mode close to softening strongly reduces the current required to reach an EP and, with the appropriate current polarity, realizes a stable EP with $Re{\lambda }_{\mathrm{EP}}<0$. At this point, the defective and highly non-normal dynamics produces pronounced directional transient amplification followed by asymptotic decay, whereas an unstable EP with $Re{\lambda }_{\mathrm{EP}}>0$ exhibits growth until nonlinear magnetization dynamics takes over. Direct integration of the LLG equation quantitatively confirms the predicted precessional dynamics, equilibrium displacement, EP spectra, mode conversion, and time-domain response. These results establish an LLG-based framework linking STT symmetry, magnetic stiffness, and current-controlled non-Hermitian magnetization dynamics.

The seminal concept of a persistent spin texture (PST) characterized by a momentum-independent spin orientation in a spin-orbit coupled system was introduced through the Rashba-Dresselhaus model in Phys. Rev. Lett. 90, 146801 (2003). By considering the combined Rashba and Dresselhaus spin-orbit coupling (SOC) interactions, the study predicted the emergence of a PST under very highly restrictive conditions of equal SOC strength. The present work introduces two low-energy effective Hamiltonians ${\mathcal{H}}_{\text{MKM}1}$ and ${\mathcal{H}}_{\text{MKM}2}$, incorporating Weyl and Dresselhaus SOC interaction terms. Remarkably, these Hamiltonians yield a persistent spin texture when the constituent SOC strengths are equal. In contrast, for unequal SOC strengths, these models accurately reproduce the recently identified partial PST (P-M2) observed in the OsSi crystal near the high-symmetry PST point located at the Brillouin-zone boundary [Nat. Commun. 16, 7999 (2025)]. By benchmarking a wide range of PST models against first-principles calculations for nonsymmorphic and noncentrosymmetric two-dimensional (2D) and bulk materials, this work uncovers a diverse range of spin-texture behaviors and highlights their distinct characteristics across different dimensionalities. This study identifies a few-layer AgI(110) as a promising 2D semiconductor platform for realizing persistent spin texture. Through rigorous theoretical analysis, this work further reveals that the PST phase can be destabilized by the application of a finite out-of-plane electric field, highlighting the sensitivity of the spin texture to the external electric-field perturbation.

Permittivity modulation in nonlocal metasurfaces provides an effective route for unlocking radiative coupling of symmetry-protected bound states in the continuum (BICs), enabling unprecedented dynamic control over resonant light-matter interactions. Here, we present a periodically poled lithium niobate metasurface platform that leverages spatially antisymmetric electro-optic responses induced by the Pockels effect to achieve continuous control of radiative coupling. Distinctively, the electro-optic asymmetry introduces an independent and continuously tunable perturbation channel, enabling postfabrication control of the radiative coupling. By interfering with the radiation amplitude induced by unintended structural asymmetry, it enables compensation of geometry-induced radiation leakage to a large extent and thereby restores high-$Q$ resonances. Concurrently, the domain-engineered architecture intrinsically embeds nonlinear optical functionality, operating as a tunable ${\chi }^{\left(2\right)}$ grating that enables large-angle ($71.4^{\circ }$) second-harmonic generation with electrically controlled emission. We demonstrate high nonlinear switching contrast exceeding 22 dB under moderate electric fields ($\le 20\mathrm{V}/\mu \mathrm{m}$), bridging high-$Q$ resonance engineering with nonlinear photonics to provide a unified platform for next-generation on-chip optical switches, dynamic filters, and frequency converters.

We evaluate the electron scattering properties in CoSi thin films having either twin (heterochiral) or nontwin (homochiral) grain boundaries using first-principles quantum transport calculations. We find that scattering across a twin grain boundary is more resistive than scattering across a nontwin grain boundary and that nontwin grain boundaries have a greater percentage of surface conduction than twin grain boundaries. This is corroborated by the transmission eigenstate profiles, which show that the surface Fermi-arc electrons can transmit past the nontwin grain boundaries between homochiral domains on the same surface without significant backscattering. In contrast, these surface electrons get scattered along the twin grain boundaries between heterochiral domains to the opposite surface, resulting in partial forward transmission and partial backscattering that yields higher grain-boundary resistivity. This work helps elucidate the complexities of electron transport in chiral topological semimetals for potential application in next-generation nanointerconnects.

The unavoidable dissipation of heat in electronic nanostructures is a crucial problem, especially when their operation requires low temperatures. It demands finding devices able to control and redirect the excess heat, ideally without perturbing the electrostatic environment. We propose three-terminal junctions working either as thermal routers or as thermal single-pole double-throw switches controlled by a single external knob. Two models are discussed based on resonant tunneling energy filters and different couplings to the heat source: (i) phase-coherent contact via a scanning tip modulates the relative amount of the two output currents via position-dependent quantum interference, (ii) coupling via a gate voltage tunable filter selectively switches one of the currents in the presence of dephasing. In the latter case, we find that the heat flow using ideal filtering is bounded by one-fourth of the open conductor current.

We derive an effective orbital-lattice model with quantum $S=1$ degrees of freedom for transition-metal compounds, providing a microscopic understanding of cluster formation driven by the cooperative interplay of spin, orbital, and lattice degrees of freedom. Motivated by the trimerized phases observed in ${\mathrm{LiVS}}_2$ and ${\mathrm{LiVO}}_2$, we consider a triangular-lattice three-orbital system with two electrons per site occupying the threefold-degenerate $t_{2g}$ manifold. Starting from a multiorbital Kanamori-Hubbard Hamiltonian, we project the low-energy sector onto the local $S=1$ triplet manifold, in which two electrons occupy different orbitals according to Hund's coupling. The resulting effective model exhibits exchange networks whose geometry is determined by the orbital configuration. However, the orbital-driven exchange interactions alone do not stabilize the experimentally observed trimer phase. We find that by incorporating ionic lattice displacements that modulate transfer integrals and induce bond-dependent exchange couplings on shortened and elongated bonds, the phase competition is qualitatively altered, leading to the robust stabilization of a trimerized ground state within a fully quantum-mechanical framework. We further show that a simplified orbital-lattice model, in which the spin-exchange energy is replaced by effective bond energies, faithfully reproduces the essential ground-state properties of the microscopic model. This reduced description enables large-scale finite-temperature simulations and reveals a rich sequence of thermal phase transitions, including first-order, second-order, and Kosterlitz-Thouless transitions into distinct spin-, orbital-, and lattice-ordered phases.

We formulate non-Hermitian Landau levels in two-dimensional systems under a complex perpendicular magnetic field. In the symmetric gauge, we derive their discretely spaced, highly degenerate complex spectra and biorthogonal eigenstates. In addition we derive analogous results in the Landau gauge and clarify the role of nonunitary gauge transformations. We find that while normalizable eigenstates exist for both gauges for $\mathrm{Re}\left(B\right)>0$, they are not always related by such a gauge transformation. A non-Hermitian Harper-Hofstadter lattice model confirms the continuum theory and reveals Gaussian wave packet dynamics governed by semiclassical equations with a complex Lorentz force, pointing to possible experimental realizations of complex magnetic fields in mechanical metamaterials or ultracold atom gases.

The parity anomaly of a single massless Dirac fermion is manifested as a half-quantized Hall response once the required parity-breaking regularization is supplied. We study the corresponding response for two-dimensional chiral Lifshitz fermions. For a node with low-energy coupling ${(q_x+\mathrm{i}{q}_y)}^N$, the Fermi-loop winding number $W=N$ gives an anomalous Hall response ${\sigma }_{xy}^{\mathrm{anom}}=(W/2)e^2/h$. We examine this mechanism in chiral multilayer Haldane models tuned to a valley-selective critical line, where a single gapless chiral Lifshitz fermion remains at the $K$ valley. For the AB, ABC, and ABCA stacks, the projected pseudospin textures give $W=2,3,4$, while Kubo calculations yield ${\sigma }_{xy}=(1,3/2,2)e^2/h$; integrated equilibrium boundary currents reproduce the same $W/2$ sequence. Six-terminal simulations with dephasing further show that the Hall conductivity is quantized at $W/2$ while the longitudinal conductivity remains finite. These results identify gapless chiral Lifshitz fermions as a higher-order, winding-controlled generalization of the parity-anomalous Hall response, distinct from a quantum anomalous Hall insulating state even when $W/2$ is an integer.