In two-dimensional systems with space-time inversion symmetry, such as $C_{2z}\mathcal{T}$, the reality condition on wave functions gives rise to real band topology characterized by the Euler class, a $\mathbb{Z}$-valued topological invariant for a pair of real bands in the Brillouin zone. In this paper, we study three-dimensional $C_{2z}\mathcal{T}$-symmetric insulators characterized by ${\overline{e}}_2$, defined as the difference in the Euler classes between two $C_{2z}\mathcal{T}$-invariant planes in the three-dimensional Brillouin zone. By deriving effective surface Hamiltonians from generic low-energy continuum Hamiltonians characterized by the topological invariant ${\overline{e}}_2$, we reveal that multiple gapless boundary states exist at the domain walls of the surface mass, which give rise to the multiple chiral hinge modes. We also show that three-dimensional insulators characterized by ${\overline{e}}_2=N$ support $N$ chiral hinge modes. Notably, due to the constraint of two occupied bands in our system, these phases are distinct from stacked Chern insulators composed of $N$ layers. Furthermore, we construct tight-binding models for ${\overline{e}}_2=2$ and 3 and numerically demonstrate the emergence of two and three chiral hinge modes, respectively. These results are consistent with those obtained from the surface theory.

In this work, we experimentally observe orientation-dependent high-harmonic spectra in rocksalt crystal MgO driven by a linearly polarized 790 nm laser, featuring distinct peaks at $0^{\circ }, {45}^{\circ }$, and ${90}^{\circ }$ that correspond to orientation angles between the laser polarization and [100] crystal axis of MgO. A localized orbital framework is developed to understand these spectral features from an atomic orbital perspective. Decomposition using atomiclike Wannier orbitals shows that low-order harmonics are primarily dominated by couplings among $\mathrm{Mg}\text{−}s, \mathrm{O}\text{−}s$, and $\mathrm{O}\text{−}p$ orbitals. Conversely, the response at higher orders is governed by $\mathrm{Mg}\text{−}p$ and $\mathrm{Mg}\text{−}d$ orbitals, with their relative contributions varying systematically with harmonic order and laser intensity. In the minimal model where only $\mathrm{O}\text{−}p–\mathrm{Mg}\text{−}s$ couplings are retained, the $\mathrm{O}\text{−}{p}_x–\mathrm{Mg}\text{−}s$ and $\mathrm{O}\text{−}{p}_y–\mathrm{Mg}\text{−}s$ channels produce yield maxima at $0^{\circ }$ and ${90}^{\circ }$, respectively, and each generates symmetric features near ${45}^{\circ }$. Their constructive superposition at ${45}^{\circ }$ results in a local maximum of the total yield at this angle. This work establishes a localized orbital picture of high-harmonic generation in crystals, bridging atomic orbital interactions and macroscopic polarization dynamics in periodic systems.

Much is known about the magnetoelectric effect of multiferroic insulators, yet little is understood about multiferroic metals. In this work, we propose a stacking engineering strategy based on monolayer magnets to construct multiferroic metals, with validation through first-principles calculations on six experimentally synthesized materials. Such multiferroic metals exhibit predominantly linear magnetoelectric response, originating from direct spin-charge interactions as a result of external field-modulated Fermi energy. This fundamentally differs from spin-charge-lattice or spin-orbit coupling mechanisms in multiferroic insulators, offering application advantages in the field of high-speed response. We derive a universal formula for understanding the magnetoelectric coupling in these multiferroic metals. Our work provides insights for exploring magnetoelectric coupling mechanisms and designing functional materials with strong magnetoelectric coupling.

Recent advances in nanothermometry have led to an extension of the Landauer-Büttiker scattering theory to include the nonlocal dissipation associated with charge transport. Such a program is implemented by describing the inelastic scattering in the connecting electrodes within an electrostatically self-consistent scheme. The restriction to quasi-one-dimensional geometries, weak excitation, and low temperature allows us to obtain general expressions of the current density and the dissipated power, valid in different regimes, for the cases of an energy-independent mean free path or an energy-independent relaxation rate. In particular, the dissipation asymmetry at both sides of a nanodevice and the conditions for observing heating spots with a local maximum of the dissipated power are formulated in terms of the key parameters that define the nanodevice and its environment.

Magnetism and topology are two major areas of condensed matter physics. The combination of magnetism and topology gives rise to more novel physical effects, which have attracted strongly theoretical and experimental attention. Recently, the concept of altermagnetism has been introduced, characterized by a dual nature: real-space antiparallel spins with zero total magnetic moment and reciprocal-space anisotropic spin polarization. The amalgamation of altermagnetism with topology may lead to the emergence of previously unobserved topological phases and the associated physical effects. In this study, utilizing a four-band lattice model that incorporates altermagnetism and spin group symmetry, we demonstrate that type-I, type-II, and type-III bipolarized Weyl semimetals can exist in altermagnetic systems. Through the first-principles electronic structure calculations, we predict four ideal two-dimensional type-I altermagnetic bipolarized Weyl semimetals ${\mathrm{Fe}}_2{\mathrm{WTe}}_4$ and ${\mathrm{Fe}}_2{\mathrm{MoZ}}_4$ $(Z=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$. More significantly, we introduce the quantum crystal valley Hall effect, a phenomenon achievable in three of these materials namely ${\mathrm{Fe}}_2{\mathrm{WTe}}_4$, ${\mathrm{Fe}}_2{\mathrm{MoS}}_4$, and ${\mathrm{Fe}}_2{\mathrm{MoSe}}_4$, when spin-orbit coupling is considered. Therefore, our work not only enriches the topological phases but also provides a material platform for studying novel topological phases in altermagnetism.

The physics of two-dimensional electron gas in a perpendicular magnetic field, i.e., the quantum Hall system, is remarkably rich. At half filling of the lowest Landau level, it has been predicted that “composite fermions”—emergent quasiparticles consisting of an electron attached to two magnetic flux quanta—experience zero net magnetic field and form a Fermi sea, dubbed composite Fermi liquid (CFL). However, despite its seemingly simple appearance, CFL is a strongly correlated quantum many-body state in disguise, and solving it in a controlled manner is extremely difficult, to the extent that the thermodynamic properties of CFL remain largely unknown. In this work, we perform state-of-the-art thermal tensor network simulations of the $\nu =1/2$ Landau level system and observe low-temperature power-law behavior of the specific heat, signaling the gapless nature of CFL. More importantly, the power is extracted to be close to $2/3$, clearly deviating from the ordinary linear-$T$ behavior of Fermi liquid, suggesting coupling between the CFs and the dynamical emergent gauge field and thereby revealing the quantum many-body nature of the CFL state.

We report polarization-resolved Raman spectroscopy of a van der Waals compound $\mathrm{GdGaI}$ that is a candidate for excitonic insulators. By combining the symmetry analysis with density functional theory calculations, we identify six Raman-active phonons. The spectra exhibit only the expected anharmonic hardening down to $4\mathrm{K}$: no additional peaks, no soft modes, and no signatures of zone folding are observed. This result indicates that any lattice distortion is below our experimental sensitivity, supporting an electronically driven origin for the band reconstruction reported by angle-resolved photoemission spectroscopy rather than an electron-phonon-driven mechanism. Moreover, we observe a pronounced circular dichroism of the $A_{1g}$ modes under an out-of-plane magnetic field. Based on symmetry considerations, we attribute this dichroic response to chiral $A_{1g}$ phonons with opposite angular momenta generated by spin-phonon coupling in the time-reversal-broken state. The temperature evolution of the degree of circular polarization further suggests that circularly polarized Raman spectroscopy detects the emergence of short-range antiferromagnetic correlations. Our results highlight $\mathrm{GdGaI}$ as a promising platform in which excitonic order, magnetism, and circularly polarized phonons can be intertwined, and demonstrate that circular-polarization Raman provides a sensitive probe of spin-phonon coupling in excitonic systems.

The Kerker effect arises from the interference between electric and magnetic multipoles, enabling directional light scattering in nanophotonics. However, conventional dielectric and plasmonic nanoparticles can only act as Kerker sources in narrow spectral regions, limiting their applicability. Here, we show that the recently discovered Mie voids overcome this limitation by supporting a broadband generalized Kerker effect spanning the whole visible range. We investigate the optical response of Mie voids under both plane-wave and dipolar excitation. For plane waves, the voids preferentially scatter light in the forward direction. Under dipolar excitation, the resulting radiation emission toward the void and beyond is suppressed due to destructive interference between the dipole field and the directional scattered field of the void. These findings identify Mie voids as versatile broadband directional sources, opening pathways for antenna design and energy harvesting at the nanoscale.

We report a systematic magnetotransport study on high-crystallinity ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ (LSNO) thin films with $x=0.20-0.24$. By conducting pulsed-field transport experiment up to 62 T, we reveal two salient features of the normal-state transport in overdoped LSNO thin films: (1) the magnetoresistance does not follow Kohler's rule but exhibits an $H$-linear behavior in the high-$H/T$ limit and (2) the normal-state $\rho \left(T\right)$ below 30 K consistently follows a $T^2$ behavior across the overdoped regime. Our results demonstrate a coexistence of $H$-linear magnetoresistance and $T^2$ resistivity in a model unconventional superconductor and provide information on the transport characteristics of the normal ground state that hosts superconductivity in infinite-layer nickelates.

We study the hole-doped Kitaev-Heisenberg chain using the density-matrix renormalization group. In the Kitaev-only limit, the bond-directional exchange itself promotes pairing, favoring spin-singlet and spin-triplet superconducting tendencies for antiferromagnetic and ferromagnetic Kitaev couplings, respectively, together with finite-size Majorana edge correlations suggestive of topological superconductivity. In the full Kitaev-Heisenberg chain, cooperative $J$- and $K$ exchanges broadly stabilize superconductivity, while competition between $J$ and $K$ induces a strong filling dependence and enables superconductivity even when both $J$ and $K$ are weak. At quarter filling, this competition produces a Mott insulator with spontaneous hopping dimerization. These results identify magnetic frustration as a common mechanism underlying superconducting and interaction-driven insulating phases in doped Kitaev systems.

We consider the relaxation of finite-wave-vector density waves in a facilitated classical lattice gas. Linear hydrodynamics predicts that such perturbations should relax exponentially, but nonlinear effects were predicted to cause subexponential relaxation via nonperturbative long-time tails [L. V. Delacretaz, SciPost Phys. 9, 034 (2020)]. We present a detailed numerical study of this effect. While our results clearly indicate the importance of nonlinear effects, we find that the wave vector dependence of the late-time relaxation is clearly inconsistent with theoretical predictions. We discuss manifestations of hydrodynamic nonlinearities in mesoscopic samples and at short times.

We define a quantum charger as an interacting quantum system that transfers energy between two drives. The key figure of merit characterizing a charger is its charging power. Remarkably, the presence of long-range interactions within the charger can induce a collective steady-state charging mode that depends superlinearly on the size of the charger, exceeding the performance of noninteracting, parallel units. Using the driven Lipkin-Meshkov-Glick model and power-law interacting spin chains, we show that this effect persists up to a critical system size set by the breakdown of the high-frequency regime. We discuss optimal work output as well as experimentally accessible initial states. The superlinear charging effect can be probed in trapped-ion experiments, and positions interacting Floquet systems as promising platforms for enhanced energy conversion.

Hybridizing multiple transverse thermoelectric effects in a single material synergistically enhances the dimensionless figure of merit for transverse thermoelectric conversion owing to the square-law characteristics of the superimposed transverse thermopowers. Here, we phenomenologically formulate the appearance of transverse magnetothermoelectric phenomena, i.e., the anomalous Nernst effect and Seebeck-driven anomalous Hall effect, in artificially tilted multilayers consisting of magnetic and thermoelectric materials, where the off-diagonal Seebeck effect originally exists due to the anisotropic composite structure. Because the contributions of the anomalous Nernst, Seebeck-driven anomalous Hall, and off-diagonal Seebeck effects to transverse thermopower have different artificial structure dependences on each other, the total thermoelectric performance is maximized by optimizing the structure to balance these effects. We confirm the appearance of these thermoelectric effects by performing a finite element analysis of transverse thermoelectric fields in artificially tilted multilayers consisting of the ferromagnetic $\mathrm{C}{\mathrm{o}}_2\mathrm{MnGa}$ Heusler alloy and thermoelectric semiconductor $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$. This work will be a guideline for designing the optimum structural parameters for superior transverse thermoelectric performance through the hybridization of spin- and magnetism-related thermoelectric phenomena in artificially tilted multilayers.

We investigate the feasibility of the macrospin approximation to account for the actual shape of soft magnetic nanoparticles (MNPs) with realistic geometries. Specifically focusing on magnetite, we use the superellipsoidal parametrization to account for a variety of shapes, with a continuous interpolation from spherical to cubic morphologies, as well as different elongations. Our procedure consists of the direct comparison between angular-dependent hysteresis loops obtained by full micromagnetic simulations, with those produced by an extended Stoner–Wohlfarth (SW) model that incorporates both the intrinsic cubic magnetocrystalline anisotropy, and an effective uniaxial contribution arising from the particle elongation. Our results show that the extended SW framework provides quantitative agreement with micromagnetics over a broad range of particle volumes and aspect ratios, indicating that the effective uniaxial term captures the dominant shape-induced contributions. The limits of validity of the macrospin description are approximately 10–60 nm for axial ratios $r>1.5$, and 20–60 nm for $1.0<r<1.5$, with the upper limit associated with the onset of nonuniform magnetization states and the lower limit reflecting micromagnetic discretization limitations. These results establish a direct connection between nanoparticle morphology and effective macrospin parameters, demonstrating the suitability of the generalized SW model for describing the magnetic response of realistically shaped MNPs.

The $A$-site magnetic spinel ${\mathrm{Co}}_3{\mathrm{O}}_4$ exhibits a simple Néel-type collinear antiferromagnetic ordering below $T_N=30$ K, accompanied by a strong linear magnetoelectric effect. Here, we report magnetization and electric polarization measurements on single crystals of ${\mathrm{Co}}_3{\mathrm{O}}_4$ up to high magnetic fields. We show that the magnetoelectric polarization undergoes a crossover from linear to nonlinear behavior with increasing magnetic field, followed by complete suppression upon reaching the field-polarized ferromagnetic state, where inversion symmetry is recovered. Our microscopic spin model, reproducing the observed field evolution of the magnetoelectric response, evidences weak anisotropy that is crucial for the effective magnetoelectric control of the antiferromagnetic state [Phys. Rev. Lett. 135, 126704 (2025)].

Periodic strain engineering in monolayer graphene provides a versatile platform to generate colossal pseudomagnetic fields and flat pseudo-Landau levels directly in a single atomic sheet. While the electronic topology and transport properties of the normal state in these systems have been extensively studied, the superconducting ground state in such strain-modulated landscapes remains an unexplored frontier. In this work, we investigate the superconducting phase of periodically corrugated graphene using a self-consistent Bogoliubov–de Gennes framework. We find that, contrary to the conventional expectation that a high density of states universally enhances pairing, the macroscopic superconducting coherence is significantly hindered in the flat-band regions. This limitation originates from strain-induced sublattice polarization, where the zero-energy electronic states are spatially segregated between the $\mathrm{A}$ and $\mathrm{B}$ sublattices. Such spatial disjointedness hampers the intersublattice coherence required for a robust pairing instability, effectively decoupling the high-density flat-band states from the superconducting condensate. Consequently, as the pairing interaction increases, the system undergoes a striking spatial crossover: Superconductivity sharply relocates from the flat-band regions to emerge as robust, quasi-one-dimensional filaments at the geometric nodes where local sublattice symmetry is restored. Our findings reveal that the spatial distribution of wave functions, governed by sublattice degrees of freedom, is a decisive factor in determining the superconducting properties of strain-engineered Dirac materials.

We develop a semiclassical theory of superconducting quasiparticles for proximity-induced superconducting systems, where spin-orbit coupling plays a critical role in shaping the quasiparticle dynamics. We reveal the structure of superconducting Berry curvatures in such systems, and derive the Berry curvature induced thermal Edelstein effect and spin Nernst effect. We calculate these two thermospin responses with model systems where Rashba spin-orbit coupling, proximity-induced superconductivity, and ferromagnetic order are coexisting.

We propose a novel protocol to realize discrete time-crystal (DTC) order in clean, periodically driven spin-$1/2$ chains. In each drive cycle, a global spin flip is followed by a two-tone flat-band segment. This flat-band segment engineers a fully degenerate Floquet quasienergy spectrum, suppresses thermalization, and stabilizes a robust period-doubled subharmonic response. Using exact time evolution, we identify a pronounced subharmonic peak at half the drive frequency in the Fourier spectrum of the order parameter, thereby providing clear evidence for the emergence of stable DTC. The resulting phase is insensitive to system size, interaction strength, and interaction range; however, it remains sensitive to spin-rotation errors (${\varepsilon }_r$), which can destabilize the subharmonic response. Compared with disorder-induced many-body localized (MBL) and disorder-free dynamically many-body localized (DMBL) DTCs, we find that the exact flat-band protocol offers a broader tunability of drive parameters, whereas MBL and DMBL-based DTCs are more resistant to ${\varepsilon }_r$. In particular, the ${\varepsilon }_r$ sensitivity can be suppressed by incorporating additional spin-spin interactions that have modest deviations from the ideal flat-band protocol. This manifests itself in a robust DTC response over a finite window of spin-coupling strengths and drive frequencies. Our results establish flat-band driving as a versatile and experimentally relevant route to DTC order in disorder-free spin systems and motivate further exploration of nonequilibrium phases.

We report on antiferromagnetic resonance experiments in bulk tetragonal NaMnAs—a room-temperature antiferromagnetic semiconductor. Our results corroborate previous ab initio studies which propose that NaMnAs is an easy-axis antiferromagnet with the Néel vector oriented along the tetragonal axis. At $B=0$, we find a single antiferromagnetic resonance line at 7 meV and associate it with a doubly degenerate ($k=0$) magnon mode. Its energy softens considerably with increasing $T$, but remains clearly visible in the data up to room temperature. From the experimental data, we estimate the single-ion anisotropy of the Mn ions in NaMnAs in the range 0.1–0.2 meV, a value that is relatively large compared to other manganese-based antiferromagnets.