Optical centers providing an optical interface play an important role in the quantum communication and information processing. For the realization of quantum networks, rare-earth ions in cavities offer a promising platform for long-distance coupling by establishing spin-photon interfaces with other qubits. Furthermore, arrays of short-range coupled rare-earth spins enable the creation of multiqubit systems and modular quantum devices. A comprehensive investigation into the interaction Hamiltonian of coupled rare-earth ions is therefore essential for exploiting their full potential in quantum technologies. In this work, we identify a pair of coupled ${\mathrm{Er}}^{3+}$ ions exhibiting magnetic dipole-dipole interaction. With a spin Hamiltonian model, we determine the full set of g tensors and J tensors, and the relative position of two ${\mathrm{Er}}^{3+}$ ions. The developed model could be applied to rare-earth spin systems and other solid-state spin systems, enabling the calculation of electronic Zeeman, quadratic Zeeman, and magnetic dipole-dipole interactions under a three-dimensional magnetic field. This work provides a comprehensive characterization of coupled optical center systems and contributes to the development of short-range coupled quantum network nodes for future quantum networks.

It is a highly nontrivial question whether magnetization is induced by a nonlinear response to a temperature gradient in systems where the linear response is forbidden by inversion symmetry. In this work, we address this issue and provide explicit examples demonstrating that such a response can indeed arise. The spin-split electron band structures induced by $d$-wave, $g$-wave, and $i$-wave altermagnets are characterized by $k^{N_X}sin{N}_X\varphi$ around the band bottom, where $N_X=2,4,$ and 6, respectively. In contrast, those of the corresponding $d^{\prime }$-wave, $g^{\prime }$ -wave, and $i^{\prime }$-wave altermagnets are described by $k^{N_X}cos{N}_X\varphi$. We show that a finite magnetization is induced in the $d^{\prime }$-wave, $g^{\prime }$-wave, and $i^{\prime }$-wave altermagnets under a second-order nonlinear response to a temperature gradient ${\left({\partial }_{x}T\right)}^2$ when the temperature gradient is linear and along either the $x$ or $y$ direction, whereas no such response occurs in the $d$ -wave, $g$-wave, and $i$-wave altermagnets. We also study the case where the direction of the temperature gradient is arbitrary. In this case, a finite magnetization is induced also in $d$-wave altermagnets but not in $g$-wave and $i$-wave altermagnets. We discuss the difference in physics between the $X$-wave and $X^{\prime }$-wave altermagnets with $X=d,g,i$ based on the tight-binding model. Furthermore, we show the emergence of magnetization as a response when the temperature profile is not linear, ${\partial }_x^{2}T\ne 0$.

Efficient transport of spin and orbital moments, and their electrical detection, are among the main challenges in spintronics and orbitronics. In magnetic insulators, these currents are mediated by magnons. In addition to carrying spin and orbital moment, the orbital motion of a magnon, combined with its magnetic moment, generates an effective electric dipole moment. Here, we develop a theoretical framework for Seebeck- and Nernst-type transport of the magnon orbital moment and its associated electric dipole moment (EDM). We identify a Drude-like scattering contribution and an intrinsic component governed by the generalized Berry curvatures of magnon bands. We show that a measurable transverse voltage generated by the EDM current provides a direct electrical detection scheme for magnon orbital transport. Applying our theory to a hexagonal altermagnet, we obtain an experimentally accessible voltage of approximately $0.4\mu \mathrm{V}$. Our results establish a concrete electrical probe of magnon orbital transport and highlight magnons as potential low-dissipation information carriers for orbitronics.

In Lieb lattices, geometric frustration and destructive interference of hopping cancels the occupation of certain sites, leading to flat-band physics. Here, we show numerically how, in the driven-dissipative Bose-Hubbard model arranged into Lieb lattices and related geometries, specific localized driving schemes can repurpose this interference to generate enhanced antibunching via a mechanism similar to the so-called unconventional photon blockade. Stochastic simulations using the positive-P method allow us to calculate occupations and second-order correlations exactly for extended lattices. We use this to optimize the parameters for the possible observation of this effect in polariton micropillar experiments. This work demonstrates the possibility of using localized driving and interference effects to generate nontrivial quantum correlations in open quantum lattice systems—specifically, producing antibunching in the dark sites of the flat-band system rather than the usual and less useful bunching.

Based on the continuum model and independent-particle approximation, this work systematically investigates the synergistic modulation effects of stacking configuration and twist angle on second-harmonic generation (SHG) in twisted bilayer graphene (TBG), twisted monolayer–bilayer graphene (TMBG), twisted double-bilayer graphene (TDBG), and twisted bilayer–trilayer graphene (TBTG). It is found that under single-photon resonance (SPR) or two-photon resonance (TPR) conditions, SHG is significantly enhanced when the incident photon energy matches the van Hove singularity (VHS) band gap. Increasing the number of stacked layers reduces the system symmetry from ${\mathrm{D}}_3$ to ${\mathrm{C}}_3$, effectively switching the dominant SHG response from out-of-plane to in-plane components and enhancing the susceptibility by approximately 50 times, in agreement with experimental values. Reducing the twist angle further enables an order-of-magnitude enhancement of the SHG intensity and a redshift of the resonance energy by increasing the density of states at the VHS while narrowing its band gap. Moreover, polarization-resolved SHG analysis directly reveals the evolution of system symmetry. The results demonstrate that interlayer charge transfer induces an inhomogeneous in-plane electron cloud distribution, breaking the inversion symmetry of the system. This activates the electric dipole response and triggers both the interband Berry curvature and the intraband term of the SHG susceptibility, which constitute the core mechanism driving the SHG response. This work elucidates stacking configuration and twist angle as central tuning degrees of freedom, providing a pathway for designing high-performance, tunable graphene-based nonlinear photonic devices.

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.