We investigate radiative heat transfer in the extreme near-field regime using a microscopic approach based on the nonequilibrium Green's function (NEGF) formalism combined with first-principles simulations of the frequency- and wave-vector-dependent dielectric function. Unlike previous studies, our first-principles simulations of the dielectric function, which determines the transmission function within the NEGF framework, are performed at the actual temperature of the media. Finite temperature effects such as phonon excitations, all-order phonon scattering, and phonon anharmonicity, which are neglected in ground-state (0 K) treatments, are directly included in our first-principles approach. Electron-phonon coupling is also incorporated indirectly within the adiabatic approximation through thermally displaced atomic configurations. Using two graphene sheets as a model system, we show that ground-state dielectric function fails to reproduce the response of the material, particularly at high temperatures and low frequencies where phonons are excited. The phonon anharmonicity increases both the real and imaginary parts of the dielectric function at low frequencies. Our simulations demonstrate that when ground-state dielectric function is used for predicting radiative conductance, an error in the range of 32–43% is obtained for a temperature of 1200 K depending on the gap size. The anharmonic effects on radiative conductance are strongest at medium temperatures and neglecting these effects results in 8.4–25.6% underestimation of the radiative conductance at 750 K. Last, we find that the gap dependence of the conductance follows a power-law behavior of $d^{-n}$, where $n$ varies slightly from 1.39 to 1.48 depending on the temperature. Our work establishes a first-principles framework that incorporates finite-temperature and anharmonic effects into microscopic theories of extreme near-field thermal radiation and demonstrates that these effects are essential for accurate modeling of radiative heat transfer in this regime.

We introduce a scheme for constructing order parameters (OPs) in translationally invariant systems by extracting generic patterns from the dominant Fock states of many-body ground states. While topological phases are traditionally characterized by nonlocal invariants, we demonstrate that our real-space OPs provide a more refined classification. In the extended Su-Schrieffer-Heeger model, we show that the standard winding number is insufficient to fully distinguish all phases; our OPs reveal a hidden substructure where each topological sector splits into two distinct phases. Beyond identifying the phase boundaries, these OPs quantify the depth of a phase, and remain robust in characterizing transitions in disordered systems. Furthermore, our approach provides a practical finite-size diagnostic for the Berezinskii-Kosterlitz-Thouless transition in the interacting spin-$\frac{1}{2}$ XXZ model. The presented framework offers a broadly applicable tool for uncovering the phase diagrams of diverse interacting and noninteracting quantum many-body systems.

The kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ provides a unique platform for studying intertwined quantum orders. Combing first-principles calculations and the Eliashberg theory of electron-phonon coupling (EPC), this work reveals axial-strain effects on superconducting properties of the kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ via EPC modulation. We demonstrate that compressive strains along distinct crystallographic directions induce contrasting phonon-mode responses: The $c$-axis compression softens M-point phonons while hardening L-point modes, whereas $ab$-plane strain directly enhances V-V orbital hybridization. These strain-induced electronic and lattice dynamics changes lead to nonmonotonic EPC evolution and monotonic suppression of superconducting transition temperature ($T_c$). Carrier doping further modulates superconductivity through dual mechanisms: Hole doping enhances EPC (λ up to 1.65) through phonon softening and Van Hove singularity (VHS) engineering, while electron doping suppresses it. Anisotropic Migdal-Eliashberg calculations indicate highly anisotropic superconducting gaps (e.g., 76.74% anisotropy under 8% $c$-axis strain), primarily governed by V $d$-orbital electrons. Moreover, self-consistent Bogoliubov–de Gennes (BdG) equations based on Wannier functions confirm that $T_c$ decreases monotonically with increasing strain, consistent with Eliashberg-theory predictions. This study establishes axial-strain tuning strategies for optimizing $T_c$ in kagome systems, providing theoretical insights for experimental manipulation of superconducting material properties.

Ultralow lattice thermal conductivity (${\kappa }_L$) is often found in halide compounds with highly anharmonic lattice frameworks, yet the structural descriptors governing phonon transport remain unclear. Here, we establish a structural framework linking octahedral configurations to phonon dynamics through two key factors: (i) halogen–halogen-related lattice coupling associated with rotational soft modes, leading to phonon spectrum decongestion, enlarged scattering phase spaces, and enhanced anharmonic phonon scattering; and (ii) local octahedral distortions that modify phonon branch separation and dispersion characteristics. Using first-principles calculations on ${\mathrm{CsPbBr}}_3$, we reveal how halogen-mediated rotational dynamics and octahedral distortions reshape the phonon landscape. Guided by these insights, we develop a high-throughput screening strategy that identifies halogen-coordinated octahedral frameworks capable of supporting rotational dynamics and quantifies intrinsic octahedral distortions using a geometric distortion factor $\rho$. This approach uncovers halide compounds with strongly distorted octahedral units and promising ultralow lattice thermal conductivity, establishing rotational soft modes and octahedral distortions as transferable structural descriptors for discovering advanced thermal management materials.

We develop a theory for the phonon magnetic moment in doped Dirac materials, treating phonons as emergent gauge and gravitational fields coupled to Dirac fermions in curved space. By classifying electron-phonon coupling into angular momentum channels of Fermi surface deformation, we show that the phonon moment arises from two mechanisms: proportional to the electron Hall conductivity through the emergent gauge field coupling, and to the Hall viscosity through the frame field coupling. Applying our theory to ${\mathrm{Cd}}_3{\mathrm{As}}_2$ with first-principles calculations, we find order-of-magnitude agreement with experiment. Our results reveal a general mechanism for dynamically generating large phonon magnetism in metals and suggest a route for probing Hall viscosity via phonon dynamics.

We theoretically investigate charge transport in a junction between a conventional superconductor and a ${\mathrm{V}}_2\mathrm{O}$-based altermagnet exhibiting distinctive spin-split quasi-one-dimensional Fermi surfaces. The altermagnet is described by a microscopically motivated seven-basis-state model with six-orbital characters that incorporates sublattice degrees of freedom associated with both V and O sites. Based on calculations performed under various boundary conditions, we demonstrate the robust emergence of specular Andreev reflection with a distinctive spin polarization. Furthermore, we propose an efficient multiterminal setup to detect this specular Andreev reflection through nonlocal conductance measurements. Our results establish ${\mathrm{V}}_2\mathrm{O}$-based altermagnets as a promising platform for realizing spin-resolved Cooper pair splitting, which is essential for generating energy-entangled electron pairs.

We propose that the superconducting diode (SD) efficiency can be significantly enhanced near the transition between two superconducting states by choosing parameters where, before the system goes normal with increasing supercurrent, it switches into a different superconducting order for one direction of the current but not for the other. This mechanism for producing high SD efficiency relies on the expectation that the critical current depends sensitively on the superconducting order. We demonstrate this explicitly by performing detailed calculations for a bilayer superconductor with an in-plane magnetic field, which admits the standard Bardeen–Cooper–Schrieffer (BCS) and orbital Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) orders as a function of the field strength. We predict a sharp peak in the SD efficiency in the FFLO state close to the transition, which arises from a complex interplay between the two superconducting orders. An implication of our study is that measuring the SD efficiency can provide fundamental insight into the nature of the BCS–FFLO transition both as a function of the magnetic field and the supercurrent.

High-$Q$ acoustic whispering-gallery modes (WGMs) support narrow size-dependent resonances, but a narrow linewidth alone does not guarantee a high-contrast radiation force because a smooth nonresonant background may remain comparable to the resonant contribution. Using acoustic Mie theory and the radiation stress tensor, we derive an exact decomposition of the in-plane force on a compressible fluid sphere with respect to a selected Mie coefficient. The force separates into a target-independent term and two target-resonant terms proportional to the real and imaginary parts of that coefficient; within an isolated-resonance window, the target-independent term forms a smooth background. Evanescent excitation reweights the incident partial waves: The enlarged tangential wave number preferentially enhances coupling to high-order WGMs, whereas spatial decay reduces the local driving amplitude. Because the target WGM benefits from this preferential coupling while the background does not, their combined action substantially increases the resonant-to-background force contrast. Near resonance, the tangential force exhibits an approximately Lorentzian profile governed mainly by the real-part channel, whereas the normal force exhibits a dispersive profile governed mainly by the imaginary-part channel. These results establish a channel-resolved mechanism for generating high-contrast, size-selective acoustic forces and provide a theoretical basis for resonance-assisted particle manipulation and sorting.

We present a high-throughput investigation of all 1062 aliovalent double half-Heusler (DHH) compositions by combining ${\mathrm{r}}^2\mathrm{SCAN}$-based density functional theory, Boltzmann transport, and a hybrid machine learning interatomic potentials MACE-assisted Slack workflow for lattice thermal conductivity. Clear sublattice-dependent trends are identified, where $X$- and $Y$-splitting generally favor the tetragonal $I\overline{4}2d$ prototype and preserve the half-Heusler's (HH) hybridization mechanism, while $Z$-splitting tends to stabilize $Pmn{2}_1$ at the prototype level but strongly perturbs the $p–d$ backbone, narrows or collapses the band gap, and greatly reduces thermodynamic competitiveness. As a result, near-hull compounds are concentrated mainly in the $X$-split and $Y$-split families, whereas the $Z$-split family is largely unstable. The thermodynamic accessibility of DHHs is further shown to correlate with both the stability of the parent HH end points and the presence of a finite semiconducting gap, indicating that stronger bonding and larger $E_{\mathrm{g}}$ generally coincide with greater stability. Transport analysis reveals that stable DHHs can reach power factors comparable to high-performance HH under heavy doping, with the optimal carrier concentration shifting systematically to higher values with increasing temperature. At a given thermal-conductivity budget, $p$-type systems outperform $n$-type ones. At the same time, the lowest lattice thermal conductivities are found for heavy-element, structurally complex compounds, confirming that DHH chemistry provides a natural route to phonon suppression. Together, these results establish a physically motivated design map for DHH thermoelectrics and identify $X/Y$-split compositions as the most promising route toward stable, high-performance materials.

We present an approach for first principles investigations on the spin-driven electric polarization in type II multiferroics. We propose a parametrization of the polarization with the parameters calculated using the Korringa-Kohn-Rostoker Green's function (KKR-GF) formalism. Within this approach the induced electric polarization of a unit cell is represented in terms of three-site parameters. Those antisymmetric with respect to spin permutation are seen as an ab initio based counterpart to the phenomenological parameters used within the inverse-Dzyaloshinskii-Moriya-interaction (DMI) model. Due to their relativistic origin, these parameters are responsible for the electric polarization induced in the presence of a noncollinear spin alignment in materials with a centrosymmetric crystal structure. Beyond this, our approach gives direct access to the element- or site-resolved electric polarization. To demonstrate the capability of the approach, we consider several examples of the so-called type II multiferroics, for which the magnetoelectric effect is observed either as a consequence of an applied magnetic field (we use ${\mathrm{Cr}}_2{\mathrm{O}}_3$ as a prototype), or as a result of a phase transition to a spin-spiral magnetic state, as for instance in ${\mathrm{MnI}}_2, {\mathrm{CuCrO}}_2$, and ${\mathrm{AgCrO}}_2$.

Amorphous strontium titanate exhibits exceptional thermal and electronic properties critical for advanced semiconductor devices. However, its lattice thermal conductivity as a bulk material has not been reported. Its underlying structural characteristics and thermal transport mechanisms remain unexplored. Herein, we perform Green-Kubo molecular dynamics and Allen-Feldman analysis across 100–1800 K using the neuroevolution potentials trained on ab initio datasets. We report a low thermal conductivity (0.40 ${\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ at 300 K) with conventional glass-like thermal conductivity behavior across the temperature range below its recrystallization onset temperature at 800 K. This low lattice thermal conductivity stems from its structural complexity and dual localization mechanisms present within the amorphous perovskite framework. High-frequency modes confined within the disordered ${\mathrm{TiO}}_6$ polyhedra and a group of low-frequency modes involved Sr atom rattling, collectively enabling up to 29% localized vibrations, which is triple that of a conventional example of amorphous silica. Structural analysis shows contracted Ti-Ti distances and disrupted Sr networks create rattling cages for phonon trapping. Our work establishes atomic-scale design principles for disorder-mediated thermal suppression in perovskite-derived glasses, providing pathways to engineer thermal-insulating materials.

Fully compensated ferrimagnetism (fFIM) represents an intriguing magnetic state characterized by spin-split bands throughout the Brillouin zone, yet zero net magnetization. Unlike conventional antiferromagnets (cAFM) or altermagnets, fFIM generally does not require stringent crystallographic symmetry constraints and can exist in a wide range of space groups. This unique feature makes it a promising platform for exploring second-order nonlinear optical responses, such as the bulk photovoltaic (BPV) effect, which typically arises only in low-symmetry systems; however, the BPV effect in fFIM remains largely unexplored. In this work, we systematically investigate the generation and modulation of the BPV effect in fFIM. Using a tight-binding model on a hexagonal lattice, we elucidate the transition from cAFM to fFIM and the corresponding evolution of the BPV response under linearly polarized light. Our results reveal that fFIM exhibits richer BPV behaviors compared to cAFM. Based on spin group and magnetic group theory, we establish the nonrelativistic and relativistic BPV generation rules in hexagonal fFIM systems, encompassing systems with both weak and strong spin-orbit coupling. These findings are validated through first-principles calculations on a realistic material. This work not only advances the theoretical understanding of nonlinear photocurrents in unconventional magnetic systems but also offers new insights for designing high-performance optoelectronic devices via symmetry engineering.

Understanding and manipulating nanoscale domain wall (DW) dynamics is a central topic in magnetism and spintronics for its promising applications in logic and memory devices. In most magnetic systems, inertia affects only transient DW dynamics, while the long-time DW motion is uniquely determined by the magnitude and direction of the applied current. Here we show that this paradigm breaks down in ferrimagnets near the angular momentum compensation point. We demonstrate that a DW can propagate steadily either forward or backward under a direct current, with the direction controlled solely by the current strength. This anomalous phenomenon originates from the inertial dynamics of an internal DW collective coordinate, which behaves as a massive object evolving in a current-dependent double-well potential. By dynamically selecting between distinct stable attractors, inertia qualitatively determines the steady-state response of DWs. The predicted reversal of DW propagation direction is robust against disorders and thermal fluctuations. Our findings establish inertia as a potential control parameter for steady spin dynamics and may provide a novel strategy for controlling magnetic solitons in spintronic systems.

We investigate the finite-size effects, energy spectra, and thermodynamics of a spin-$\frac{1}{2}$ trimer, a three-sided star tetramer, and tetrahedron clusters with Heisenberg and bond-dependent Kitaev exchange. Using exact diagonalization, we compare the isotropic-exchange case with the corresponding Heisenberg-Kitaev clusters in an applied magnetic field. The Kitaev term lifts degeneracies, hybridizes states with different total-spin character, and produces nonlinear field-dependent eigenvalues associated with avoided crossings. These spectral changes generate field-driven cluster transitions, including first- and second-order ground-state transitions associated with level crossings and continuous ground-state evolution. They also redistribute finite-level Schottky weight in the magnetic heat capacity and can produce additional low-temperature heat-capacity features when the ratio $K/J$ is large. The results provide analytic cluster benchmarks for identifying how bond-dependent symmetric anisotropic exchange modifies spectra, entropy, and heat-capacity response in molecular-magnet and cluster-based spin systems. It should be noted that while these calculations provide insight into the individual Kitaev interaction, finite-size effects mean this does not fully carry over to bulk systems that exhibit quantum spin liquid behavior.