Exotic quantum phenomena are often found to occur in spin systems that exhibit low-dimensional magnetism. By combining nuclear magnetic resonance, neutron-scattering, and muon-spin spectroscopy ($\mu \mathrm{SR}$) techniques, we report a rare instance of strongly frustrated two-dimensional (2D) magnetism in a three-dimensional (3D) hexagonal perovskite. Here, ${\mathrm{Ba}}_2{\mathrm{La}}_2{\mathrm{MnTe}}_2{\mathrm{O}}_{12}$, a triangular-lattice magnet, is shown to undergo a magnetic transition at $T_{\mathrm{N}}\approx 4.4\mathrm{K}$, below which the manganese moments form a ${120}^{\circ }$ AFM order within the $ab$ plane while staying disordered along the $c$ axis. This exotic ground state, which exhibits ideal 2D magnetism, is highly consistent with the persistently strong spin fluctuations and the large internal field distributions revealed by zero-field $\mu \mathrm{SR}$. Further, the 2D magnetism also leads to a significant frustration, much larger than that of most known magnetically ordered, frustrated systems. Our work on ${\mathrm{Ba}}_2{\mathrm{La}}_2{\mathrm{MnTe}}_2{\mathrm{O}}_{12}$ not only challenges the interpretations of magnetic order in other 3D hexagonal perovskites, but it also provides insight into how the dimensionality affects the exotic magnetic states.

Low-dimensional quantum magnets provide an ideal platform to explore spin-lattice coupling-mediated quantum correlations, which give rise to emergent quasiparticle excitations. The antiferromagnetically coupled spin-1/2 trimer chain of copper ions in ${\mathrm{Na}}_2{\mathrm{Cu}}_3{\mathrm{Ge}}_4{\mathrm{O}}_{12}$ (NCGO) hosts high-energy spin excitations of different species, whose energy scales overlap with those of lattice vibrations. Here, we report a comprehensive temperature-dependent Raman spectroscopic study performed between 80 and 400 K. The dynamic spin susceptibility, as obtained from the analysis of the broad spectral background, reveals the emergence of quasiparticle excitations below 170 K. We further identify an unusual crossover of phonon dynamics when the material transits from a normal paramagnetic state to a correlated quantum magnetic state. A power law dependence of the integrated Raman susceptibility of the phonon modes, $I_{{\chi }^{″}}^i\sim {|T-T_c|}^{\beta }$, is observed with the critical temperature $T_c=167\pm 1\mathrm{K}$, and critical exponent $\beta =0.24\pm 0.02$. The combined results obtained from the broad spectral background and sharp phonon peaks further indicate that the phonon renormalization observed across the crossover is driven by dynamic spin states. Additionally, statistical correlations among phonon energy eigenvalues, quantified through matrix-norm and power-test analyses of 200 spectra recorded at 80 K, reveal an unexpected linear correlation among phonon modes, also indicating that the collective lattice response is governed by spin correlations. These findings establish NCGO as a model system for investigating cooperative spin-lattice coupling and critical scaling behavior of phonon dynamics in low-dimensional magnetic materials.

The recent discovery of a superconducting transition temperature $T_{\mathrm{c}}$ of 96 K in the Sm-doped Ruddlesden-Popper bilayer nickelate $\mathrm{L}{\mathrm{a}}_{3-x}\mathrm{S}{\mathrm{m}}_x\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_{7-d}$ under high pressure has attracted considerable attention [F. Li et al., Nature (London) 649, 871 (2026)]. However, the underlying mechanism of the effects of chemical pressure induced by such doping remains unclear. In this work, we systematically investigate the crystal and electronic structures of $\mathrm{L}{\mathrm{a}}_2\mathrm{SmN}{\mathrm{i}}_2{\mathrm{O}}_7$ under pressure using first-principles calculations and extend our study to $\mathrm{L}{\mathrm{a}}_{2}R\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ ($R=\mathrm{Pr}$, Nd) to elucidate the general influence of chemical pressure. Our results indicate that chemical pressure intensifies octahedral rotational distortion, inducing anisotropic in-plane lattice evolution and elevating the critical pressure for phase transition, while it compresses the out-of-plane apical Ni-O bond length and reduces octahedral regularity, thereby enhancing the density of states of the Ni $d_{z^2}$ orbital at the Fermi level, which is favorable for superconductivity. Chemical pressure adjusts the electron occupation of the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals by creating a crystal field with smaller $e_g$ splitting.

The phase transition of ice under temperature and pressure fields attracts a great deal of attention from scientific research. However, there are many research gaps on more multiple extreme fields on ice phase transition. Here, using nonequilibrium ab initio molecular dynamics (AIMD), we systematically studied the effects of electric field, pressure, and temperature acting on the ice, and discussed the phase transition reduced by the combination of these extreme fields. Specifically, a phase, absent in zero electric field and named ice VIII′ in this paper, is discovered by applying an electric field to ice VIII, ice VII, and ice X, with high a possibility to be obtained in the laboratory. Later when the electric field further strengthens, superionization occurs as a unidirectional electrical breakdown with detailed analysis of the electric field intensity and ionic conductivity at these extreme multiple fields.

Although the classification of crystalline materials can be generally handled by momentum-space-based approaches, topological classification of aperiodic materials remains an outstanding challenge, as the absence of translational symmetry renders such conventional approaches inapplicable. Here, we present a numerically efficient real-space framework for classifying parity-based ${\mathbb{Z}}_2$ topology in aperiodic systems based on the spectral localizer framework and the direct computation of the sign of a Pfaffian associated with a large sparse skew-symmetric matrix. Unlike projector-based or momentum-space-based approaches, our method does not rely on translational symmetry, spectral gaps in the Hamiltonian's bulk, or gapped auxiliary operators such as spin projections, and instead provides a local, energy-resolved topological invariant accompanied by an intrinsic measure of topological protection. A central contribution of this work is the development of a scalable sparse factorization algorithm that enables the reliable determination of the Pfaffian's sign for large sparse matrices, making the approach practical for realistic physical materials. We apply this framework to identify the quantum spin Hall effect in quasicrystalline class AII systems, including gapless heterostructures, and to diagnose fragile topology in a large $C_2\mathcal{T}$-symmetric photonic quasicrystal. Overall, our results demonstrate that the spectral localizer, combined with efficient sparse numerical methods, provides a unified and robust tool for diagnosing parity-based topological phases in aperiodic electronic, photonic, and acoustic materials where conventional band-theoretic indexes are inapplicable.

Topological charge pumping (TCP) has been extensively investigated both theoretically and experimentally in recent years. However, the role of nonlocal electron-phonon ($e$-ph) interactions in this phenomenon remains incompletely understood. In this work, we incorporate nonlocal $e$-ph coupling into an extended Rice-Mele model and systematically investigate its influence on the pumping dynamics. We demonstrate that, in the adiabatic regime where the driving frequency is far below the electronic energy scale, quantized charge pumping remains robust against $e$-ph coupling up to a finite threshold. Notably, this threshold decreases with increasing driving frequency, signaling a frequency-tunable breakdown of quantization. The underlying mechanism stems from $e$-ph interaction-induced lattice relaxation, which dynamically renormalizes the electronic band structure and drives the system into a nonadiabatic regime. A hallmark of this transition is an $e$-ph coupling-dependent timescale governing the collapse of quantization, accompanied by a transient reversal of the pumped charge. In the strong-coupling limit, the effective pumping paths are entirely destroyed, resulting in a complete suppression of charge pumping. Overall, our results highlight the crucial role of lattice degrees of freedom in governing TCP.

Materials with anisotropic thermal conductivity enable directional heat transfer and are critical for advanced thermal management. Transition-metal pentatellurides, especially $\mathrm{HfT}{\mathrm{e}}_5$, have attracted increasing interest due to the recently reported record-high in-plane thermal conductivity anisotropy ratio ($\sim 3.5$) at room temperature. However, the microscopic mechanisms underlying this extreme anisotropy, particularly the lattice dynamics and phonon properties, have not been systematically investigated. Here, we reveal that the strong bonding inhomogeneity—featuring robust chainlike bonds along the $a$-axis and weak interchain bonds along the $c$-axis—leads to pronounced anisotropy in phonon dispersions, group velocities, and mean free paths. Notably, low-energy optical phonons along the $a$-axis are strongly activated, acquiring high group velocities and long mean free paths, and contribute up to 57% of the total thermal conductivity, while $c$-axis optical phonons remain flat with limited transport. As a result, optical phonons contribute nearly twice as much as acoustic phonons to the in-plane thermal conductivity anisotropy. These findings reveal the crucial role of optical phonons in directional heat transport and provide a framework for designing materials to precisely control heat flow.

Domain wall motion underpins emerging spintronic technologies, such as high-speed racetrack devices and THz logic, and accelerating walls quickly is a key challenge on the path to faster devices. Recent experimental advances introduced magnetic materials with nonuniform composition, allowing angular momentum compensation points and fast domain wall motion, although acceleration of domain walls in these materials remains poorly understood. Here, we show that spatial variation of exchange and anisotropy not only pushes the wall toward a lower wall surface tension region, but also modifies its inertial mass, giving rise to a variable-mass relativistic dynamics. We find another force, originating from the magnon velocity gradient, that dominates as the wall velocity approaches the magnon speed. Our results identify domain walls in nonuniform magnets as a playground for relativistic physics with variable mass and limiting speed.

While the anomalous Hall effect (AHE) has been extensively studied in the past, analyzing its mechanism continues to be a critical topic in condensed matter physics, especially in unconventional magnetic materials with noncollinear or noncoplanar magnetic structures. Here, we explore the AHE in the noncoplanar magnet ${\mathrm{Cr}}_{0.27}{\mathrm{NbS}}_2$ and identify the intrinsic mechanism as its dominant origin using a refined scaling method. Conventional scaling analysis fails in this system as it treats the magnetization $M$ as a constant, thereby misattributing its influence to scattering (${\rho }_{xx}$) and obscuring the true AHE mechanism. With the field and temperature dependence of magnetization explicitly incorporated, the proper scaling relationship is restored, allowing the exponent $\alpha \approx 1.91$ to be accurately determined and thus confirming the intrinsic origin. Our study provides a detailed analysis of AHE in ${\mathrm{Cr}}_{0.27}{\mathrm{NbS}}_2$ and demonstrates that analyzing AHE mechanisms in such complex magnetic systems requires careful modifications to account for magnetization effects. Such adaptations, which account for the influence of the nonsaturated magnetic state on the Hall effect, are crucial to prevent the misinterpretation of scaling failure as the emergence of extrinsic origins, thereby ensuring the accurate extraction of the intrinsic Berry curvature contribution from the complex magnetic background.

We investigate spin-orbit torque effects in epitaxial ${\text{La}}_{0.67}{\text{Sr}}_{0.33}{\text{MnO}}_3$ (LSMO) films via spin-torque ferromagnetic resonance. In the absence of any extrinsic spin source, spin currents with ${\sigma }_y, {\sigma }_z$, and ${\sigma }_x$ polarizations are observed in a single LSMO layer. Decomposing the response within the Kubo linear response formalism reveals that the ${\sigma }_y$ component is composed of both interband and intraband terms, whereas the ${\sigma }_z$ and ${\sigma }_x$ components are dominated by the interband term. The interband contribution is closely linked to the thickness-dependent strain and Mn-$e_{\text{g}}$ level splitting. This effect is attributed to a redistribution of the spin Berry curvature, induced by a structural gradient of octahedral distortions and rotations that breaks inversion symmetry. In contrast, the intraband contribution is attributed to a Rashba-like response in the inversion-symmetry-broken regions. These results indicate that octahedral distortions and rotations in epitaxial LSMO can reshape the Mn-$e_{\text{g}}$ band structure and interband transitions, thereby modifying the intrinsic spin-transport tensor and making the spin polarization components sensitive to structural details. Our work establishes a link between structural distortion and spin current generation in epitaxial LSMO films and provides a basis for designing field-free magnetization switching in single-layer oxide spintronic devices.

We propose a model describing the formation of both conventional and dual Shapiro steps in small Josephson junctions. According to our model, dual Shapiro steps occur at relatively low frequency of the microwave signal and low microwave power, whereas conventional steps occur in the opposite limit of high frequency and power. The crossover between these two regimes is controlled by a single parameter—the effective relaxation time of the environment. Our model takes into account the effect of a large inductor in the bias circuit, which has been used in recent experiments to protect the junction from the high-frequency noise of the environment. We predict the possibility of observing both types of steps in the same sample. Our model describes the I-V curves observed in the experiments with reasonable accuracy, thus opening the possibility of quantitatively fitting experimental data.

We propose a generalization of the Filoche-Mayboroda localization landscape that extends the theory well beyond the static, elliptic, and Hermitian settings while preserving its geometric interpretability and recovering the original framework as a special case. Using the positive operator $H^{†}H$, we obtain a geometric diagnostic of localization without computing any eigenstate. Singular-value collapse reveals spectral instabilities and the skin-effect geometry associated with right-eigenstate accumulation. In driven systems, we establish a precise connection between near-gap closings in the singular-value spectrum of the Sambe operator and dynamical localization. The Sambe formulation captures coherent destruction of tunneling, while topological zero modes are accurately identified in both one- and two-dimensional models. Benchmarks on Hatano-Nelson chains, driven two-level systems, and driven Aubry-André-Harper models confirm quantitative accuracy. The resulting framework provides a focused geometric diagnostic for singular non-Hermitian and Floquet physics, with favorable computational scaling for multifrequency driven systems.

Cobalt-based systems provide a unique platform in which strong spin–orbit coupling entangles spin, charge, orbital, and lattice degrees of freedom, leading to pronounced multiferroic behavior. In the present study, magnetic-ordering-enhanced ferroelectricity is observed in flux-grown polar ${\mathrm{Co}}_3{\mathrm{BPO}}_7$ single crystals. Synchrotron x-ray diffraction confirms a noncentrosymmetric polar Cm structure, where ${\mathrm{Co}}^{2+}$ ions form buckled hexagonal layers along the $b$ axis. Magnetic susceptibility and heat-capacity measurements reveal strong anisotropy with two antiferromagnetic transitions at T${}_{\mathrm{N}1}\approx 27\mathrm{K}$ and T${}_{\mathrm{N}2}\approx 15\mathrm{K}$. Neutron diffraction reveals a noncollinear magnetic structure mainly confined to the $ac$ plane, with a finite canting component along the $b$ axis. The three Co ions form a triangular network connected by alternating corner- and edge-sharing units, generating quasihexagonal rings in the $ab$ plane. Dielectric constant, pyroelectric, and second-harmonic-generation measurements show clear magnetoelectric anomalies at both magnetic transitions. Synchrotron x-ray diffraction further identifies local lattice distortions near T${}_{\mathrm{N}1}$, indicating significant magnetoelastic coupling. Berry-phase calculations based on density-functional theory suggest that the absence of inversion symmetry, together with the frustrated triangular Co lattice, stabilizes a noncollinear antiferromagnetic structure. Magnetic ordering enhances spin–spin correlations, activates spin–lattice coupling, and induces a finite Dzyaloshinskii–Moriya interaction, resulting in modulation of the electric polarization.

Chirality in magnetic systems gives rise to a wide range of exotic phenomena, yet its influence in $S=1$ chains remains largely unexplored. Herein, we present a comprehensive experimental study of a chiral antiferromagnetic $S=1$ chain, $\left[\mathrm{Ni}\left(\mathrm{pym}\right){\left({\mathrm{H}}_2\mathrm{O}\right)}_4\right]{\mathrm{SO}}_4·{\mathrm{H}}_2\mathrm{O}$ (pym = pyrimidine), where the Ni(II) octahedral orientation exhibits a fourfold chiral periodicity. Muon-spin rotation measurements indicate the onset of long-range magnetic order below $T_{\mathrm{N}}=1.82\left(1\right)\mathrm{K}$. Neutron diffraction measurements reveal a chiral antiferromagnetic order driven by a chiral modulation of the easy-axis anisotropy direction, rather than the typical scenario of Dzyaloshinskii-Moriya interactions, geometrical frustration, or higher-order interactions. Inelastic neutron scattering measurements reveal dispersive spin-wave excitations well described by linear spin-wave theory, with Hamiltonian parameters $J_0=6.81\left(1\right)\mathrm{K}$ (intrachain exchange), $J_{1\mathrm{a}}^{\prime }=-0.09\left(1\right)\mathrm{K}$ (interchain exchange), and $D=-3.02\left(1\right)\mathrm{K}$ (easy-axis single-ion anisotropy). These parameters are further validated by Monte Carlo simulations of the magnetization. Additionally, the inelastic neutron scattering data reveal multiple dispersionless bands, suggesting the presence of further excitations beyond the scope of our linear spin-wave theory.

We report a comprehensive investigation of the excitation spectrum of ${\mathrm{ErFeO}}_3$ orthoferrite by means of time-of-flight neutron spectroscopy. The spectrum consists of two distinct components: strongly dispersive spin wave excitations of the ${\mathrm{Fe}}^{3+}$ sublattice spanning $\approx 9$–65 meV, and crystal electric field (CEF) excitations of ${\mathrm{Er}}^{3+}$ ions below 36 meV. The observed spin wave dispersions and spectral weight are well captured within linear spin wave theory, enabling extraction of the key Fe-Fe exchange parameters. Low-energy incident neutrons with their enhanced energy resolution, further revealed the dispersive character and splitting of Kramers-degenerate CEF levels. We show that the dispersion is caused by the exchange coupling between ${\mathrm{Er}}^{3+}$ ions, while the degeneracy is lifted by interactions between the ${\mathrm{Er}}^{3+}$ and ${\mathrm{Fe}}^{3+}$ sublattices. We further explore the influence of dipolar and antisymmetric exchange interactions with the focus on the magnetic ground state of ${\mathrm{ErFeO}}_3$, with particular attention to the low-temperature spin arrangement. Taken together, our results provide a detailed account of the spin dynamics in ${\mathrm{ErFeO}}_3$ and reveal a hierarchy of interactions scales characteristic for orthoferrites.

We present the results of a resonant x-ray-diffraction experiment, resolving both charge and spin textures in the intermetallic topological magnet $\mathrm{Eu}{\left({\mathrm{Al}}_{1-x}{\mathrm{Ga}}_x\right)}_4$ ($x$ = 0.1). Below $\approx 75$ K the system develops a charge-density wave (CDW) with propagation vector ${\mathbf{k}}_{\text{CDW}}\approx (0,0,0.18)$. The CDW order parameter grows monotonically on cooling until $\approx 15$ K, when a sudden decrease in the CDW amplitude occurs. Pairs of magnetic satellites of the (0, 0, 8) Bragg reflection corresponding to two distinct domains, ${\mathbf{k}}_1$ = ($\pm {\delta }_{\text{m}}$, 0, 0), ${\mathbf{k}}_2$ = (0, $\pm {\delta }_{\text{m}}$, 0), ${\delta }_{\text{m}}=0.2002\left(4\right)$ were studied at the Eu $L_{\text{3}}$ edge, appearing below $T_{\text{N}}$ = 14.8 K. Our measurement of $T_{\text{N}}$ is exactly coincident with the sudden drop in the CDW amplitude, which suggests strong coupling between the charge and spin orders, as observed in other compounds of the $\mathrm{Eu}{\left({\mathrm{Al}}_{1-x}{\mathrm{Ga}}_x\right)}_4$ series. Azimuthal measurements were consistent with a single helical spin arrangement having an elliptical envelope of ${\mu }_{\text{Y}}/{\mu }_{\text{Z}}$ = 1.19(6) for the ${\mathbf{k}}_2$ domain, and a tilted helical (helicoidal) spin arrangement for the ${\mathbf{k}}_1$ domain, with ${\mu }_{\text{Y}}/{\mu }_{\text{Z}}$ = 1.14(4) and ${\mu }_{\text{X}}/{\mu }_{\text{Z}}$ = 0.20(2) that may be hidden for the ${\mathbf{k}}_2$ domain due to multiple subdomains. Temperature evolution of the magnetic satellite intensities in linear and circularly polarized light found the respective ratio to be invariant with temperature, suggesting a single helicoidal magnetic phase throughout the measured temperature range. This behavior is unlike the $x$ = 0 material, in which a spin-density wave forms first, transitioning to a helical ground state on cooling through intermediate phases. Future theoretical work on the Eu electronic ground state, supported by related experiments, will help understand the effects of Ga substitution on the evolution of the magnetic structure.

Coupled optical and magnetic excitations can give rise to remarkably strong magneto-optic responses. This is particularly evident in van der Waals magnets, such as the antiferromagnet CrSBr, where excitons and magnons emerge from the same electronic orbitals. While previous work has primarily focused on uncovering the origin of the resulting exciton-magnon interactions, the influence of photonic effects has received comparatively little attention. Here, we use numerical simulations to disentangle exciton-magnon coupling from the exciton-mediated magnon-photon interactions observed in optical experiments. By simulating realistic scenarios using parameters determined by experiments, we illustrate the strong dependence of these interactions on photonic interference and dispersion effects near excitonic resonances. Such effects shape the optical response to coherent magnons and make it intrinsically nonlinear in the magnon-induced exciton energy shift. Thermal magnons, which have a particularly pronounced impact on excitons, are found to even produce qualitatively different trends in optical signatures. Depending on weak or strong coupling of excitons and photons, the same exciton-magnon interaction can lead to a redshift of optical modes, a nearly vanishing response, or their blueshift. Finally, we demonstrate steps towards optimizing the multiparameter problem of efficient magnon-photon transduction using a machine-learning approach.

Correlated magnon excitations in topologically nontrivial systems remain largely unexplored experimentally. Here, we report that 10% La substitution in localized-insulator $\mathrm{EuBiT}{\mathrm{e}}_3$ yields single crystals of $\mathrm{L}{\mathrm{a}}_{0.1}\mathrm{E}{\mathrm{u}}_{0.9}\mathrm{BiT}{\mathrm{e}}_3$ that simultaneously host antiferromagnetic order ($T_N=7\mathrm{K}$) and a topological Weyl-semimetallic state. Magnetic susceptibility and low-temperature specific-heat measurements reveal a field-dependent minimum at $T_M=3\mathrm{K}$ and a finite magnon gap that softens with increasing magnetic field-signatures of magnon gap formation. Electrical transport, including planar Hall measurements, follows semiclassical Boltzmann theory yet violates conventional Lorentz-force behavior, reflecting nontrivial Berry curvature effects. Angle-resolved photoemission spectroscopy directly visualizes linearly dispersive bulk bands crossing the Fermi level and isolated two-fold-degenerate Weyl nodes. These results establish $\mathrm{L}{\mathrm{a}}_{0.1}\mathrm{E}{\mathrm{u}}_{0.9}\mathrm{BiT}{\mathrm{e}}_3$ as a versatile platform for investigating the interplay between correlated magnetic excitations and topological Weyl phases.

We report a field-switchable first-order antiferromagnetic-antiferromagnetic (AFM-AFM) phase transition in single-crystalline $\mathrm{H}{\mathrm{o}}_3\mathrm{C}{\mathrm{u}}_4\mathrm{S}{\mathrm{n}}_4$, which differs from the widely studied AFM-FM and FM-FM first-order magnetic transitions. Electrical resistivity and magnetic susceptibility measurements reveal sharp, discontinuous jumps and hysteresis between the two AFM states, with a large positive magnetoresistance change exceeding 55%, a value that far exceeds the typical magnitude of intrinsic magnetoresistance ($\sim 0.1\%-10\%$) in conventional antiferromagnetic materials. Notably, this AFM-AFM transition can be fully switched by a modest magnetic field of only 0.4 T, in stark contrast to conventional AFM-FM first-order transitions, which typically require $\sim 2-5$ T external magnetic fields. This work constructs the detailed magnetic phase diagram of this system, reveals the critical role of sinusoidal spin reorientation in the giant magnetoresistance effect, and provides an experimental platform for studying low-field-tunable antiferromagnetic phase transitions.