We formulate the problem of near-field radiative heat transfer as an effective quantum scattering theory for excitations of the matter. Built from the same ingredients as the semiclassical fluctuational electrodynamics, the standard tool to handle this problem, our construction makes manifest its relation to the Landauer-Büttiker scattering framework, which appears only implicitly in the fluctuational electrodynamics. We show how to construct the scattering matrix for the matter excitations and give a general expression for the energy current in terms of this scattering matrix. We show that the energy current has an important nondissipative contribution that can dominate the finite-frequency noise while being absent in the average current. Our construction provides a unified description of near-field radiative heat transfer in diverse physical systems.

CeRhSn is a valence fluctuating heavy-fermion metal with a twisted Ce-kagome lattice, displaying zero-field quantum criticality, previously associated with geometrical frustration. The partial substitution of Rh by Pd in ${\mathrm{CeRh}}_{1-x}{\mathrm{Pd}}_x\mathrm{Sn}$ enlarges the unit-cell volume, suppresses valence fluctuations, decreases the Kondo temperature, and stabilizes a possible long-range antiferromagnetic (AFM) ordered ground state with $T_N=0.8$ K at $x=0.5$. Previous thermodynamic and spectroscopic measurements for $x=0.1$ suggested a quantum critical spin liquid. We report low-temperature dilatometry and magnetization measurements on ${\mathrm{CeRh}}_{0.9}{\mathrm{Pd}}_{0.1}\mathrm{Sn}$ and compare with published low-$T$ specific heat data. The absence of a Grüneisen parameter divergence excludes a conventional quantum criticality scenario. Instead, the weak power-law divergences signal non-Fermi-liquid (NFL) behavior, according to a disorder-driven quantum Griffiths phase scenario. At low temperatures, a negative thermal expansion is found in fields above approximately 0.5 T and the NFL scaling breaks down, probably due to the polarization of AFM correlations.

We report ${}^{73}\mathrm{Ge}$ nuclear quadrupole resonance (NQR) and magnetic resonance (NMR) spectroscopy in the heavy-fermion quantum-critical ferromagnet ${\mathrm{CeRh}}_6{\mathrm{Ge}}_4$. NQR and NMR spectral measurements at the two nonequivalent Ge sites reveal electric field gradient tensors and the directions of their principal axes relative to the hexagonal basal plane. The spin-lattice relaxation rate $1/T_1$ experiments reveal a clear critical slowing down approaching the ferromagnetic transition. $1/T_1$ in the paramagnetic state is found to be predominantly caused by fluctuating $4f$-local moments. The Knight shift shows Curie-Weiss behavior at high temperature and a deviation from this below $T^{*}\approx 25\mathrm{K}$ possibly due to a mixture of crystalline electric field effects and Kondo screening. Order-parameter-like behavior of hyperfine fields at the Ge sites and ferromagnetic signal enhancement are observed in Zeeman-perturbed NQR, with uniform ferromagnetic order and a small ordered moment of $\approx 0.26{\mu }_{\mathrm{B}}/\mathrm{Ce}$ confined within the $ab$ plane. The ordered moment shows a notable in-plane magnetic stiffness against out-of-plane radio-frequency fields and has an (XY-type) in-plane isotropic nature. Our results reveal a strong easy-plane anisotropy of $4f$-electron moment and suggest an involved interplay of hybridization and local moment physics in this quantum critical heavy-fermion ferromagnet.

Magnetite (${\mathrm{Fe}}_3{\mathrm{O}}_4$) nanoparticles exhibit size-dependent magnetic and thermal properties crucial for spintronics, thermoelectrics, and hyperthermia applications, yet the nanoscale behavior of magnons and phonons remains poorly understood. Combining time-of-flight inelastic neutron scattering and numerical simulations, we reveal a universal mechanism of confinement-driven quasiparticle renormalization in ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles. In 8-nm particles, optical phonons soften by 0.5 meV and significantly broaden, while acoustic magnons exhibit suppressed group velocities (from $14000\mathrm{m}{\mathrm{s}}^{-1}$ to $10000\mathrm{m}{\mathrm{s}}^{-1}$) due to surface-induced exchange disorder. Heterogeneous spin environments, combining bulklike ($J$) and surfacelike ($J^{\prime }<J$) interactions, quantitatively explain spectral broadening and magnon softening. These findings establish finite-size confinement as a general paradigm for engineering spin and thermal transport in nanoscale systems, with direct implications for enhancing spin-wave lifetimes in spintronic devices and phonon engineering in thermoelectrics.

We identify a universal functional form that governs anticoncentration in random quantum circuits—one that holds across diverse circuit architectures and depths, and crucially remains valid even at finite system sizes and shallow depth. We support this claim through analytical results for ensembles of random tensor-network states and random-phase models. This compact, universal expression for the output bitstring probability distribution is fully characterized by just two fitting parameters, as validated through extensive numerical simulations. Our findings underscore the pivotal role of finite-size and finite-depth effects in shaping anticoncentration, and they introduce a practical framework for benchmarking quantum devices using shallow circuits, thereby enabling validation of systems significantly larger than previously accessible.

We report thermodynamic, neutron diffraction, and inelastic neutron scattering measurements on ${\mathrm{Cs}}_2{\mathrm{RuO}}_4$, a member of the celebrated family of frustrated magnets ${\mathrm{Cs}}_{2}M{X}_4$ ($M$ = Cu, Co, $X$ = Br, Cl). Unlike the previously studied members, it is based on $4d$ transition metal ions with $S=1$. Mapping out the $H\text{−}T$ magnetic phase diagram reveals an unusual continuous spin-flop-like phase transition associated with a quantum critical point within the antiferromagnetically ordered phase. A quantitative analysis of the complex magnetic excitation spectrum measured in zero field allows us to derive a model magnetic Hamiltonian for this compound. Its main feature is a frustration of magnetic anisotropy on a level that is much higher than in any of the previously studied species. This frustration naturally explains the peculiar phase transition observed.

We propose that three-dimensional (3D) layered octagonal quasicrystals can host magnetic-field tunable Möbius insulators and various higher-order topological insulators (HOTIs), enabled by the interplay of quasicrystalline symmetry and magnetic order. By constructing a minimal model based on stacked Ammann-Beenker tilings with magnetic exchange coupling and octagonal warping, we demonstrate that an A-type antiferromagnetic (AFM) configuration yields a topological phase protected by an effective time-reversal symmetry $\mathcal{S}=\mathcal{T}{\tau }_{1/2}$. Breaking $\mathcal{S}$ via an in-plane magnetic field induced canting of the AFM order while preserving a nonsymmorphic glide symmetry ${\mathcal{G}}_n={\tau }_{1/2}{\mathcal{M}}_n$ leads to Möbius-twisted surface states, realizing a Möbius insulator in an aperiodic 3D system. Furthermore, we show that the quasicrystal with a general magnetic configuration supports multiple HOTI phases characterized by distinct hinge mode configurations that can be switched by rotating the magnetic field. A low-energy effective theory reveals that these transitions are driven by mass kinks between adjacent surfaces. Our work establishes a platform for realizing symmetry-protected topological phases unique to quasicrystals and highlights the tunability of hinge and surface states via magnetic control.

We probe the possible double-Weyl state in cubic ${\mathrm{SrSi}}_2$ using optical spectroscopy. The complex optical conductivity was measured in a frequency range from 70 to 22 000 ${\mathrm{cm}}^{-1}$ at temperatures down to 10 K at ambient pressure. The optical response of ${\mathrm{SrSi}}_2$ can be well separated into the intraband (free carriers) and interband contributions. Additionally, four infrared-active phonons are detected. As follows from the optical spectra, the free-carrier density decreases with decreasing temperature, consistent with an activation behavior. Experimental interband conductivity juxtaposed with ab initio calculations shows that conventional density-functional theory fails to describe the electronic structure of ${\mathrm{SrSi}}_2$ in the vicinity of the Fermi level. A semilocal exchange-correlation potential allows a much better agreement with the experiment, resulting in the trivial (gapped) band structure of ${\mathrm{SrSi}}_2$. The direct gap estimated from the measurements is approximately 40 meV.

We experimentally study the dispersion relation of waves in a thin quasi-two-dimensional (2D) defect layer with periodic nanopores that sits on a 3D photonic band-gap crystal made from silicon by CMOS-compatible methods. The nanostructures are probed by momentum-resolved broadband near-infrared imaging of $p$-polarized reflected light as a function of off-axis wave vectors. We identify surface defect modes at frequencies inside the 3D photonic band gap with a narrow relative linewidth ($\mathrm{\Delta }\omega /\omega =0.028$), which are absent in defect-free 3D photonic band-gap crystals. We calculate the dispersion of the states with relevant mode symmetries using a plane-wave-expansion supercell method, with structural parameters directly extracted from scanning electron microscope images. The calculated bands match very well with the measured data. The slope of the dispersion curves of the surface defect states is negative in one off-axis direction, corresponding to backward-propagating waves in that direction where the phase velocity and the group velocity point in opposite directions, as confirmed by finite-difference time-domain simulations. We also present a didactic and analytic model of a 2D grating sandwiched between vacuum and a negative real effective ${\varepsilon }^{\prime }<0$ that mimics the 3D photonic band gap. The model's dispersion agrees with the experiments and with the full theory and shows that the backward propagation is caused by the surface grating. We discuss possible applications, including a device that senses the output direction of photons emitted by embedded quantum emitters in response to their emission frequency.

The combination of two-dimensional materials into heterostructures offers new opportunities for the design of optoelectronic devices with tunable properties. However, computing electronic and optical properties of such systems using state-of-the-art methodology is challenging due to their large unit cells. This is particularly so for highly precise all-electron calculations within the framework of many-body perturbation theory, which come with high computational costs. Here, we extend an approach that allows for the efficient calculation of the noninteracting polarizability, previously developed for plane wave basis sets, to the (linearized) augmented plane wave method. This approach is based on an additive ansatz, which computes and superposes the polarizabilities of the individual components in their respective unit cells. We implement this formalism in the $G_0{W}_0$ module of the $\mathtt{exciting}$ code and implement an analogous approach for BSE calculations. This allows the calculation of highly precise optical spectra at low cost. So-obtained results of the quasiparticle band structure and optical spectra are demonstrated for bilayer ${\mathrm{WSe}}_2$ and pyridine@${\mathrm{MoS}}_2$ in comparison with exact reference calculations.

Valley degrees of freedom in two-dimensional (2D) materials promise revolutionary advances in information processing, yet their practical implementation faces fundamental challenges. While hexagonal transition-metal dichalcogenides require external fields to break valley degeneracy, anisotropic materials such as tin sulfide (SnS) offer intrinsically nondegenerate valleys addressable with linearly polarized light—but understanding valley-specific dynamics remains elusive. Here, we demonstrate that resonant Raman scattering unveils a direct fingerprint of valley identity through strong reorganization of exciton-phonon coupling. At the $X_1$ valley (1.37 eV), the $A_g^3$ breathing mode dominates with fourfold enhancement over $A_g^4$, while this hierarchy completely inverts at the $X_3$ valley (1.68 eV) where $A_g^4$ shows sixfold stronger coupling. This valley-specific coupling originates from the distinct orbital characters, as revealed by our density functional theory calculations: $p_x$ orbitals at $X_1$ couple efficiently to symmetric breathing motions, whose symmetric compression/extension modulates the $p_x\text{−}{p}_x$ overlap. Conversely, the mixed $s\text{−}p$ orbitals at $X_3$ favor complex displacement patterns. Beyond conventional Raman modes, we observe resonant activation of infrared-active phonons through Fröhlich coupling, with valley-dependent polarization selection rules and activation energies of 4.6–13.2 meV. Power-dependent measurements reveal valley-specific saturation behaviors, with $X_3$ saturating at three times lower carrier densities than $X_1$ due to differences in band curvature. These findings establish phonon scattering as an intrinsic probe of valley physics, enabling optical identification and potentially manipulation of valley states. Our results demonstrate that exciton-phonon coupling in anisotropic 2D materials fundamentally encodes valley information, opening pathways for phonon-mediated valley control in next-generation valleytronic devices.

We revisit the stability of the superconducting state within mean-field theory in the presence of repulsive pairing interactions, focusing on multiband systems where such channels naturally arise. We show that, when repulsion is present, the self-consistent BCS solution appears as a saddle point of the conventional mean-field free energy, casting doubt on its physical stability, but that this apparent pathology simply reflects the use of a non-variational functional. Recasting the problem with Bogoliubov's variational principle restores a free energy that is bounded from below and places the BCS solution at a genuine minimum. Using a two-band toy model relevant to iron-based superconductors, we demonstrate the stability of the $s_{\pm }$ state and clarify how projection schemes that rely only on the interaction matrix can misidentify the attractive eigenmode that drives pairing. Our results clarify the instability issue highlighted by Aase et al. [Aase, Johnsen, and Sudbø, Phys. Rev. B 108, 024509 (2023)] and provide a consistent foundation for analyzing fluctuations in the presence of repulsive interactions.

The effect of a constant electric field on two-photon absorption in a semiconductor is calculated using an independent-particle theory. The theoretical framework is an extension of a theory of the one-photon Franz-Keldysh effect [J. K. Wahlstrand and J. E. Sipe, Phys. Rev. B 82, 075206 (2010)]. The theory includes the effect of the constant field, including field-induced coupling between closely spaced bands, and with it we calculate the optical absorption perturbatively. Numerical calculations are performed using a 14-band $\mathbf{k}·\mathbf{p}$ band structure model for GaAs. For all nonzero tensor elements, field-enabled two-photon absorption (TPA) below the band gap and Franz-Keldysh oscillations in the TPA spectrum are predicted, with a generally larger effect in tensor elements with more components parallel to the constant electric field direction. Some tensor elements that are zero in the absence of a field become nonzero in the presence of the constant electric field and depend on its sign. Notably, these elements are linear in the electric field to lowest order, and may be substantial away from band structure critical points at room temperature and/or with a nonuniform field. Electric-field-induced changes in the carrier injection rate due to interference between one- and two-photon absorption are also calculated. The electric field enables this bichromatic coherent control process for polarization configurations where it is normally forbidden by crystal symmetry, and also modifies the spectrum of the process for configurations where it is allowed.

We report time-domain measurements of indirectly coupled resonators in open systems. We examine a coupled LRC circuit and a cavity-magnon-polariton system, each with resonators coupled through a shared transmission line. In both cases, time-domain measurements directly resolve the temporal evolution of hybridized eigenmodes, thereby revealing non-Hermitian dynamics. To unify the platforms, we formulate a general model that uses circuit analysis and temporal coupled-mode theory and derive the corresponding S-parameter expressions. Moreover, recent theoretical work has shown that frequency-domain absorption is more effective than transmission for identifying eigenmodes in open systems. Our work provides an experimental confirmation of this prediction which agrees with the direct time-domain observations.

The discovery of high-$T_c$ superconductivity in sulfur trihydride (${\mathrm{H}}_3\mathrm{S}$) over a decade ago opened an exciting era of research on superconducting superhydrides; however, in spite of extensive studies, there remain unresolved issues concerning the structural stability and superconductivity of ${\mathrm{H}}_3\mathrm{S}$. Most conspicuous are large discrepancies between theoretical and experimental pressures for stabilizing the optimal high-$T_c$ phase and between calculated and measured $T_c$ values. Here, using first-principles calculations, we show that deviatoric stress and associated strain, omnipresent in experiments yet omitted in past theoretical treatments, can notably impact stability and $T_c$ of ${\mathrm{H}}_3\mathrm{S}$. These findings unveil stress-altered properties of highly compressed ${\mathrm{H}}_3\mathrm{S}$, offering a possible explanation for the disparity between theory and experiment. Moreover, this study showcases deviatoric stress as a viable mechanism for modulating material properties, which has important implications for high-pressure research across multiple scientific fields where nonhydrostatic pressure conditions are prevalent.

In this work, we generalize several three-dimensional ${\mathbb{Z}}_2$ stabilizer models—including the X-cube model, the three-dimensional toric code, and Haah's code—to their ${\mathbb{Z}}_N$ counterparts. Under periodic boundary conditions, we analyze their ground state degeneracies and topological excitations and uncover behaviors that strongly depend on system size. For the X-cube model, we identify excitations with mobility restricted under local operations but relaxed under nonlocal ones derived from global topology. These excitations, previously confined to open boundaries in the ${\mathbb{Z}}_2$ model, now appear even under periodic boundaries. In the toric code, we observe nontrivial braiding between string and point excitations despite the absence of ground state degeneracy, indicating long-range entanglement independent of topological degeneracy. Again, this effect extends from open to periodic boundaries in the generalized models. For Haah's code, we find new excitations—fracton tripoles and monopoles—that remain globally constrained, along with a relaxation of immobility giving rise to lineons and planons. These results reveal new forms of topological order and suggest a broader framework for understanding fracton phases beyond the conventional ${\mathbb{Z}}_2$ setting.

Following the topological classification of electronic phases, interest has grown in materials with unique electronic or magnetic properties driven by topology and interactions. Here we report that the topologically nontrivial mixed valent intermetalllic ${\mathrm{EuPd}}_3{\mathrm{S}}_4$ undergoes long-range charge ordering at $T_{\mathrm{CO}}=340$ K, wherein $J=7/2{\mathrm{Eu}}^{2+}$ and Van Vleck $J=0{\mathrm{Eu}}^{3+}$ ions on a body-centered-cubic lattice separate into two interpenetrating simple cubic sublattices. The reduced symmetry transmutes eightfold double Dirac states into fourfold Dirac states and leads to a simple cubic Heisenberg antiferromagnet with G-type antiferromagnetic order for $T<T_{\mathrm{N}}=2.85\left(6\right)$ K. While time reversal symmetry is broken, its combination with nearest neighbor lattice translation can form a nonsymmorphic symmetry preserving the fourfold Dirac point. The application of a magnetic field yields a spin flop transition at the lowest temperatures but, as a consequence of the extreme isotropy of Eu, that phase transition turns into a crossover at higher temperatures. Our work demonstrates how charge order modifies topology in ${\mathrm{EuPd}}_3{\mathrm{S}}_4$ and exposes an archetypal simple cubic Heisenberg antiferromagnet.

Magnetic hopfions are noncollinear spin textures that are characterized by an integer topological invariant, called the Hopf index. The three-dimensional magnetic solitons can be thought of as a tube with a twisted magnetization that has been closed at both ends to form a torus. The tube consists of a magnetic whirl called an in-plane skyrmion or bimeron. Although hopfions have been observed by microscopy techniques, their detection remains challenging as they lack an electronic hallmark so far. Here we predict a three-dimensional orbital Hall effect caused by hopfion textures: When an electric field is applied, the hopfion generates a transverse current of orbital angular momentum. The effect arises due to the local emergent field that gives rise to in-plane and out-of-plane orbital Hall conductivities. This orbital Hall response can be seen as a hallmark of hopfions and allows us to distinguish them from other textures, such as skyrmioniums, that look similar in real-space microscopy experiments. While the two-dimensional topological invariant of a skyrmion determines its topological Hall transport, the unique three-dimensional topological orbital Hall effect can be identified with the three-dimensional topological invariant that is the Hopf index. Our results make hopfions attractive for spin-orbitronic applications because their orbital signatures allow for their detection in devices and give rise to large orbital torques.

The rational combination of existing magnetic topological compounds presents a promising route for designing topological materials. We report the synthesis and comprehensive characterization of the layered quaternary intergrowth compound ${\mathrm{Eu}}_2{\mathrm{CuZn}}_2{\mathrm{As}}_3$, which combines structural units of two known magnetic topological materials, EuCuAs and ${\mathrm{EuZn}}_2{\mathrm{As}}_2$. ${\mathrm{Eu}}_2{\mathrm{CuZn}}_2{\mathrm{As}}_3$ exhibits an antiferromagnetic ground state with successive magnetic transitions: quasi-two-dimensional ordering at $T_{\mathrm{M}}=29.3\mathrm{K}$, long-range antiferromagnetic ordering at $T_{\mathrm{N}}=19\mathrm{K}$, and spin reorientation at $T_{\mathrm{SR}}=16.3\mathrm{K}$. The stepwise magnetic transitions manifest as plateaulike anomalies in the heat capacity. These transitions originate from multiple superexchange pathways and periodic variation of interplane Eu-Eu distances in the intergrowth structure. Charge transport shows a pronounced resistivity increase above $T_{\mathrm{N}}$ followed by minimal change below the ordering temperature. Magnetic fields rapidly suppress this resistivity rise, yielding significant negative magnetoresistance. Remarkably, ${\mathrm{Eu}}_2{\mathrm{CuZn}}_2{\mathrm{As}}_3$ inherits the nonlinear anomalous Hall effect characteristic of its parent compounds. Energy evaluations of collinear spin configurations reveal a lowest-energy state with ferromagnetic coupling between Eu planes in EuCuAs units while maintaining antiferromagnetic coupling within ${\mathrm{EuZn}}_2{\mathrm{As}}_2$ units. The corresponding electronic structure displays potentially topologically nontrivial features. Our work demonstrates the efficacy of structural hybridization for discovering alternative magnetic topological materials and establishes a general strategy for materials discovery.

Considering the similarity of the real-space configurations for the opposite spin sublattices in both antiferromagnets (AFMs) and altermagnets (AMs), the relationship between them should be profound. In this work, we demonstrate that AFMs and AMs can be connected with spin groups and their subgroups. Consequently, the breaking of the combined inversion or translation operation with time-reversal symmetry $(\mathcal{PT}$ or $\mathbf{t}\mathcal{T})$ in AFMs will induce transition from AFM to AM. We systematically list all collinear spin point groups and space groups that can realize the transition for the three types of AFMs: $\mathcal{PT}$, $\mathbf{t}\mathcal{T}$, and $\mathcal{PT}\text{−}\mathbf{t}\mathcal{T}$. Moreover, we propose that Floquet engineering using circularly polarized light and surface cutting engineering are effective approaches to break $\mathcal{PT}$ and $\mathbf{t}\mathcal{T}$ symmetries of AFM, respectively, achieving the transition. Interestingly, the features and magnitude of AM spin splitting can be tuned by adjusting various parameters of Floquet engineering. In our work, we not only establish a theoretical framework for the transition from AFM to AM but also provide practical approaches utilizing the achievements in AFMs for 100 years to obtain AMs, significantly expanding the scope of AM materials for both theoretical studies and future practical applications.