Antiferromagnetic transition-metal oxides provide robust platforms for spintronic and magnonic applications, where control of magnetic exchange interactions is essential for tailoring spin dynamics. Molecular adsorption at organic/inorganic interfaces offers a promising route to chemically engineer these interactions. We investigate how molecular adsorption modifies surface superexchange interactions in antiferromagnetic transition-metal oxides. Using density functional theory+U calculations, we study prototypical interfaces formed by ${\mathrm{C}}_{60}$ and cobalt-tetraphenylporphyrin (CoTPP) adsorbed on NiO(001) and CoO(001) and extract exchange coupling constants $J$ from broken-symmetry total-energy calculations mapped onto a Heisenberg model. For clean surfaces, we obtain $J\approx -30\mathrm{meV}$ for NiO(001) and $J\approx -21\mathrm{meV}$ for CoO(001). Upon molecular adsorption, the magnitude of $J$ increases to $-31/-32\mathrm{meV}$ for NiO and to $-27/-30\mathrm{meV}$ for CoO, corresponding to enhancements up to $9\mathrm{meV}$ for CoTPP/CoO(001). Orbital-resolved analysis reveals that the strengthening of superexchange correlates with a directional redistribution of charge within the transition-metal $d$ manifold, characterized by a redistribution of charge involving enhanced occupation of in-plane $\sigma$ and out-of-plane $\pi$-type orbitals aligned with the TM–O–TM and TM–molecule–TM superexchange pathways, accompanied by depletion of out-of-plane $\sigma$ and in-plane $\pi$ orbitals. While only two representative molecules and two oxides are considered here, the consistency of the observed trends across chemically distinct systems suggests that the proposed orbital-repopulation mechanism may apply more broadly to related organic/antiferromagnetic-oxide interfaces.

Antiferromagnetic materials have great potential for spintronic applications at terahertz (THz) frequencies. However, in contrast to ferromagnets, experimental investigations of antiferromagnets are often challenging due to a lack of straightforward external control of the Néel vector $\mathit{L}$ and suitable probes. Here, we study an AFM|FM stack consisting of an antiferromagnetic metal layer (AFM) of the novel material ${\mathrm{Mn}}_2\mathrm{Au}$ and a ferromagnetic metal layer (FM) of ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$. To characterize the AFM|FM stack as a function of the quasistatic ${\mathit{B}}_{\mathrm{ext}}$, we perform quasistatic as well as THz-pump magneto-optic probe experiments. Our results demonstrate that AFM and FM are exchange-coupled, and that $\mathit{L}$ of the AFM can be set by the simple application of an external in-plane magnetic field ${\mathit{B}}_{\mathrm{ext}}$. We identify ultrafast signal components that can consistently be explained by the in-plane antiferromagnetic magnon mode excited by fieldlike Néel spin-orbit torque (NSOT). Remarkably, we find that the ${\mathit{B}}_{\mathrm{ext}}$- and THz-pump-induced changes in the optical response of the sample are dominated exclusively by the spin degrees of freedom of AFM. Nonmagnetic signal contributions are minor. We fully calibrate the magnetic circular and magnetic linear optical birefringence of AFM and extract the efficiency of the NSOT. Finally, by selective excitation of domains with different orientations of $\mathit{L}$, we are able to determine the relative volume fraction of $0^{\circ }, {90}^{\circ }, {180}^{\circ }$ and ${270}^{\circ }$ domains during the quasistatic reversal of $\mathit{L}$ by ${\mathit{B}}_{\mathrm{ext}}$. Our insights are an important prerequisite for future studies of ultrafast coherent switching of spins by THz NSOT and show that THz-pump magneto-optic-probe experiments are a powerful tool to characterize magnetic properties of antiferromagnets.

Chiral magnets with Dzyaloshinskii–Moriya interaction host topological spin textures that generate emergent transport. We report a comprehensive study of ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$, a less-understood member of the ${\mathrm{T}}_{1/3}\mathrm{M}{\mathrm{S}}_2$ chiral helimagnet family. Small-angle neutron scattering confirms a chiral helimagnetic ground state with a long helical period of 300 nm, indicating weak DMI. Under a $c$-axis field, the system evolves through a chiral conical phase (CCP) before reaching the forced ferromagnetic state; a pronounced topological Hall effect (${\rho }_{xy}^T\sim 70$ nΩ cm) emerges in the CCP. Detailed analysis shows that THE in CCP phases is dominated by a fluctuation-driven mechanism: thermal magnon excitations generate net scalar spin chirality even when static $〈\chi 〉$ vanishes. The intrinsic lattice chirality ($\mathrm{P}{6}_{3}22$) and DMI break left/right magnon degeneracy, allowing a longitudinal field alone to produce an imbalance. This accounts for the strong temperature dependence, boundary enhancement, and comparable topological Hall conductivity ${\sigma }_{xy}^T$ ($\sim 30{\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$) of ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ versus well-known CSL ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ ($\sim 6.5{\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$) despite much weaker DMI in the former. Our results establish ${\mathrm{Mn}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ as a distinct platform for fluctuation-driven topological transport in weakly DMI, strongly anisotropic chiral magnets.

The dynamics of current-driven skyrmions are crucial for applications in spintronics and data storage. However, inevitable random defects in materials introduce uncontrollable factors affecting skyrmion mobility. In this study, we investigate the critical dynamics of current-driven skyrmions under a voltage-controlled Rashba effect in the two-dimensional ferromagnet with quenched disorder. Using the nonstationary dynamic approach, we accurately determine critical currents and exponents for various Rashba parameters. The theoretical analysis establishes an upper limit for the critical current, which depends solely on the disorder strength and the skyrmion topological number and agrees well with numerical simulations. Notably, when the Rashba parameter is large, a directional locking phenomenon emerges, where skyrmions exhibit absolute transverse motion within a specific driving range above the critical current. Furthermore, leveraging the phase transition mechanisms, we design an all-electrically controlled multiport skyrmion-based device and a skyrmionic synapse. Our results demonstrate an efficient method to control skyrmions in disordered materials via phase transitions, emphasizing the potential of skyrmions in computing and storage devices.

The cobalt-based honeycomb magnet ${\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2$ (BCAO) has recently emerged as a promising platform for frustrated magnetism beyond conventional paradigms. Neutron-scattering experiments and first-principles calculations have revealed an unexpected double-zigzag (dZZ) magnetically ordered ground state, whose microscopic origin remains under active debate. Here, we revisit this problem within a ferroantiferromagnetic $J_1–J_3$ Heisenberg model on the honeycomb lattice using a generalized Schwinger-boson mean-field theory that treats ferromagnetic and antiferromagnetic interactions on equal footing. This approach, combined with exact diagonalization, allows us to demonstrate the emergence of the dZZ phase in a narrow parameter range, stabilized by quantum fluctuations through an order-by-disorder mechanism, in good agreement with recent density-matrix renormalization-group results. We further characterize the associated magnetic excitations and discuss their relevance to recent inelastic neutron-scattering measurements on BCAO.

Flat-band superconductors provide a regime in which kinetic energy is quenched, so that pairing is governed primarily by interactions and quantum geometry. We investigate characteristic superconducting length scales in all-flat-band systems under the assumptions of time-reversal symmetry and spatially uniform pairing, focusing on the size of the lowest-lying two-body bound state, the average Cooper-pair size, and the zero-temperature coherence length in two-band Hubbard models. Using the Creutz ladder and the $\chi$ lattice as representative examples, we show that both the two-body bound-state size and the many-body Cooper-pair size remain finite and small in the weak-coupling limit, being controlled by the quantum metric of the flat bands. By contrast, the coherence length exhibits qualitatively distinct behavior, diverging in the dilute limit and in the vicinity of insulating regimes. These results demonstrate that, in flat-band superconductors, the pair size and the coherence length are fundamentally distinct physical quantities and highlight the central role of band geometry in shaping superconducting length scales when kinetic energy is quenched.

We theoretically analyze two-dimensional coherent spectroscopy (2DCS) signals for disordered superconductors in two limits: one is the narrow-band limit with sinusoidal pulse waves and the other is the broad-band limit with delta-function pulses. While the 2DCS signal in the narrow-band limit is related to the third-order nonlinear susceptibilities ${\chi }^{\left(3\right)}(3\mathrm{\Omega };\mathrm{\Omega },\mathrm{\Omega },\mathrm{\Omega })$ (third harmonic generation) and ${\chi }^{\left(3\right)}(\mathrm{\Omega };\mathrm{\Omega },\mathrm{\Omega },-\mathrm{\Omega })$ (ac Kerr effect), we find that in the broad-band limit the signal along the diagonal and horizontal lines in the two-dimensional frequency space is related to another nonlinear susceptibility ${\chi }^{\left(3\right)}(\mathrm{\Omega };\mathrm{\Omega },0,0)$ (dc Kerr effect). We numerically evaluate those susceptibilities for a lattice model of superconductors based on the BCS mean-field theory and self-consistent Born approximation for impurities. The 2DCS signals in the narrow-band and broad-band limits show threshold and resonance behaviors at the superconducting-gap frequency, respectively, whose physical origin is discussed in light of quasiparticle and Higgs-mode excitations.

We theoretically demonstrate a gate-tunable superconducting spin valve effect (SVE) in a van der Waals (vdW) heterostructure composed of a monolayer superconductor (S) sandwiched between two ferromagnetic (F) monolayers (F/S/F). By electrostatically gating the ferromagnetic layers to modulate their chemical potentials, the system can be continuously tuned between the standard, inverse, and triplet (nonmonotonic) SVE regimes within the same device. This tunability originates from the gate-controlled hybridization between the superconducting and ferromagnetic electronic spectra, which determines the effective exchange field induced in the S layer. Furthermore, we reveal that gating enables exotic, non-BCS temperature dependencies of the superconducting order parameter, including reentrant superconductivity, bistable states, first-order phase transitions, and the emergence of superconductivity at finite temperatures. Our results establish vdW F/S/F trilayers as a versatile and highly controllable platform for superconducting spintronics, where external gate voltages can selectively activate different spin-valve functionalities and unconventional superconducting states.

We theoretically study nonequilibrium superconductivity in voltage-biased normal metal–superconductor–normal metal (NSN) junctions, focusing on the effects of lead-coupling asymmetry and impurity scattering. Using the Keldysh Green's function technique, we extend the thermal-equilibrium mean-field BCS theory to the case in which the system is out of equilibrium, to analyze superconducting properties in the nonequilibrium steady state. We find that, in close analogy with the thermal-equilibrium case, the inhomogeneous nonequilibrium Fulde-Ferrell-Larkin-Ovchinnikov (NFFLO) state induced by nonequilibrium electron distributions is highly sensitive to impurity scattering, whereas the uniform nonequilibrium BCS (NBCS) state remains robust against nonmagnetic impurities. Moreover, lead-coupling asymmetry is also found to suppress the NFFLO phase and to split the NBCS phase into two distinct regimes, characterized by the presence or absence of a chemical-potential imbalance between quasiparticles and the condensate. We identify a phase transition or a crossover between these two NBCS states, as well as parameter regimes exhibiting bistability. Our results provide a unified microscopic understanding of nonequilibrium superconductivity in NSN junctions under experimentally relevant conditions and are expected to provide a theoretical framework applicable to a broad class of nonequilibrium superconducting hybrid structures.

The pair density wave (PDW) exemplifies intertwined orders in strongly correlated systems. A recent discovery of superconductivity in a quarter-metal state [T. Han et al., Nature (London) 643, 654 (2025)] offers the first experimental system where a pure PDW without uniform superconductivity is suspected, offering a unique opportunity to examine the consequences of intertwined orders. A pure two-dimensional PDW supports an unusual fractional excitation as its topological defect (TD). A TD simultaneously winds the phase of the Cooper pair and distorts the amplitude modulation—a dual role reflecting its intertwined character. As a vortex, a TD carries fractional vorticity of $\frac{1}{3}h/2e$, whose movement would cause resistance. As a crystalline defect, a TD can be sourced by charge disorder in the system. We show that experimentally observed resistive switching can originate from mobile TDs, while a small magnetic field will restore zero resistance by blocking their motion. The resulting resistive state exhibits extreme anisotropy and a Hall response, with the Hall angle determined by the angle between the current and the TD's Burgers vector. These features will serve as confirmation of the dual identity of topological defects as emblems of PDW order.

Recent angle-resolved photoemission spectroscopy (ARPES) and density functional theory plus Hubbard $U$ ($\mathrm{DFT}+U$) studies revealed that a heavy-fermion superconductor ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ exhibits Van Hove singularities and the Dirac point near the Fermi level $E_{\mathrm{F}}$, which are key signatures of strong-correlation effects and quantum geometry. We have constructed a two-dimensional 12-orbital Dirac-Anderson model as an effective model for ${\mathrm{CeRh}}_2{\mathrm{As}}_2$. The band structure and Fermi-surface topology of the Dirac-Anderson model agree well with the ARPES data and the $\mathrm{DFT}+U$ calculations. We show that the quantum geometry strongly favors magnetic-monopole fluctuations because of the Dirac point at the $M$ point. By solving the linearized Éliashberg equation, we demonstrate that the $B_{1u}$ and $B_{2g}$ representations, spin-triplet states originating from the Dirac point, exhibit the leading superconducting instabilities. By comparing the random-phase approximation and the fluctuation-exchange approximation, we further demonstrate that strong-correlation effects mitigate the influence of quantum geometry. The phase diagram of ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ under pressure is discussed in connection with the theoretical results.

Kagome superconductors featuring topologically nontrivial band structures have attracted extensive research interest. FeSn and CoSn is an interesting kind of kagome material with intrinsic magnetism, which suppresses the emergence of superconductivity. Here, we theoretically predict a type of 1:1 kagome $M\mathrm{Sn}$ ($M=\mathrm{transition}$ metal), which exhibits intrinsic superconductivity and nontrivial band topology by first-principles calculations. Among twenty-seven candidates, $M\mathrm{Sn}$ ($M=\mathrm{Mo}$, Hf, Nb, Ta, W, Ti) are theoretically identified as both dynamically and thermodynamically stable. Five nonmagnetic $M\mathrm{Sn}$ ($M=\mathrm{Mo}$, Hf, Nb, Ta, W) exhibit phonon-mediated superconductivity. Especially, the $d$ orbital bands display Dirac points and van Hove singularities near the Fermi level, which contribute to the emergence of topology and the electron-phonon coupling (EPC). More interestingly, MoSn, HfSn, and NbSn show nontrivial topological band structure at the Fermi level. Thus, the predicted $M\mathrm{Sn}$ establish a platform integrating superconductivity and topological order.

Ferroelastic twin walls in centrosymmetric perovskites can host emergent polar and magnetic properties forbidden in the bulk. We use density functional theory calculations to study the geometry and magnetic properties of ferroelastic domain walls in orthorhombic ${\mathrm{CaMnO}}_3$, which belongs to the most common perovskite space group, $Pnma$. At the wall, the inherent inversion symmetry breaking induces local polar distortions dependent on the wall geometry, which couple to the magnetic order through the octahedral distortions. Noncollinear calculations reveal enhanced out-of-plane magnetic moments on the $\mathrm{Mn}$ atoms and a local, finite magnetization confined to the wall. Strain fields across twin walls thus give rise to coexistence of polarization and magnetization as well as magnetoelectric response that is absent and symmetry forbidden in bulk ${\mathrm{CaMnO}}_3$. We propose that magnetoelectric coupling and coexisting polarization and magnetization can emerge at twin walls in bulk centrosymmetric antiferromagnets.

Predicting plastic deformation across the spectrum of structural order, from crystalline to amorphous solids, remains a grand challenge. Coarse-grained equivalent stiffness (CGES), derived from the local dynamical matrix, is introduced as a broadly applicable parameter for mechanical stability. Its spatial variation effectively pinpoints “soft zones” susceptible to plastic rearrangements. Across six systems ranging from single crystals with dislocations to disordered polycrystals, quasicrystals, and amorphous solids, CGES spatially correlate with local plastic rearrangements, accurately capturing dislocation cores, grain boundaries, and shear transformation zones. In single crystals, CGES gradients deterministically pinpoint dislocation cores where plasticity is fully localized. For the four disordered systems, quantitative analysis shows that plastic events are statistically concentrated within CGES-identified soft zones, with occurrence probabilities 3–7 times higher than in the bulk. Moreover, local eigenvectors align with plastic rearrangements' directions, elucidating microscopic deformation pathways. Within the athermal quasistatic regime studied here, CGES offers an efficient structural descriptor for identifying plasticity-prone regions without prior loading, thereby helping to clarify the microscopic origins of localized failure in diverse solids.

Recent laser-shock experiments on an H–He mixture containing $11\%$ helium (atomic fraction) have suggested the presence of an immiscibility region inside Jupiter. Reflectivity measurements were used as the primary diagnostic of H–He demixing, with discontinuities in the optical reflectivity proposed as a signature of phase separation under conditions relevant to Jupiter's interior. Here, we investigate shock-compressed H–He using ab initio molecular dynamics simulations with optical properties evaluated within the Kubo–Greenwood formalism. The equation of state and ionic configurations were obtained using the thermal ${\mathrm{Tr}}^2$ SCANL meta-GGA exchange–correlation (XC) functional, while optical properties were computed using the recently developed RS-KDT0 range-separated thermal hybrid XC, which provides state-of-the-art accuracy for band-gap predictions in the warm dense matter regime. The calculated reflectivity shows overall good agreement with experimental measurements; however, no discontinuity is observed at elevated temperatures. Moreover, the reflectivity predictions for the mixed system are consistent with the experimental measurements in the temperature range where the mixture is inferred to be demixed. These results suggest that reflectivity alone may not provide a unique or sensitive diagnostic of H–He demixing at low helium concentrations under these conditions.

The dynamical behavior of field-induced ferroelectric phase transitions in compositions of $(1-x)\mathrm{Pb}\left({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}\right){\mathrm{O}}_3\text{−}x{\mathrm{PbTiO}}_3$, called PMN-PT, near the morphotropic phase boundary (MPB) was investigated using several different external electric-field application protocols. Our results show that PMN-PT compositions near the MPB exhibit phase transition dynamics that differ markedly from those of compositions far below the MPB. We demonstrate that the electric-field history has a notable impact on the field-induced transition temperature $T_C$, zero-field-cooling delay time ${\tau }_{\mathrm{ZFC}}$, and induced polarization $P_c$ gained or lost in the transition. Furthermore, we show that under specific field-temperature conditions, PMN-PT can retain a memory of its electric-field history and use it to kinetically accelerate ferroelectric ordering. An explanation of the key differences in phase transition dynamics between MPB-proximal and MPB-distant compositions is proposed and contextualized within the literature.

This paper investigates wavepacket dynamics in non-Hermitian lattice systems and reveals a surprising phenomenon: The simultaneous propagation of two distinct wavefronts, one traveling at the non-Hermitian velocity and the other at the Hermitian velocity. We show that this dual-front behavior arises naturally in systems governed by a pseudo-Hermitian Hamiltonian. Using the paradigmatic Hatano-Nelson model as our primary example, we demonstrate that this coexistence is essential for understanding a wide array of unconventional dynamical effects, including abrupt “non-Hermitian reflections”, sudden shifts of Gaussian wavepackets, and disorder-induced emergent packets seeded by the small initial tails. We present analytic predictions that closely match numerical simulations. These results may offer new insight into the topology of non-Hermitian systems and point toward measurable experimental consequences.

Magnets with isotropic easy-plane symmetry host Goldstone modes that can be leveraged for efficient spin transport. Here, we present a time-resolved optical polarimetry technique that allows us to detect and characterize such low-frequency modes, and use it to observe the Goldstone mode in the multi-$\mathit{Q}$ broken helix phase of ${\mathrm{EuIn}}_2{\mathrm{As}}_2$. The strength of our technique comes from the ability to distinguish between nematic and magnetization dynamics in order to yield information about the mode structure, in addition to its frequency. We find that the nearly uniform spin precession characteristic of a Goldstone mode is realized only when a small magnetic field is used to unpin the broken helix from local strain generated during crystal growth. In this regime, the mode frequency scales linearly with the applied field due to the ground state ${\mathrm{C}}_{2z}$ symmetry of the broken helix. Our work shows how optical polarimetry can be used to study the Goldstone modes of complex magnets.

Modulating magnetism in two-dimensional (2D) materials is of great importance for the development of spintronics. Although surface adsorption has been demonstrated as an effective approach for tuning electronic and magnetic properties, its application in 2D magnetic materials is still emerging. In this work, we demonstrate that surface adsorption can robustly induce multiple magnetic phase transitions in Néel antiferromagnetic $M\text{P}{X}_3$ monolayers. By selectively adsorbing representative metal (Be, Ca) and highly electronegative nonmetal (O, F) atoms on $M\text{P}{X}_3$ with their corresponding energetically favored configuration, the antiferromagnetic ground state can be transformed into ferromagnetic, altermagnetic, ferrimagnetic, or fully compensated ferrimagnetic states, accompanied by significant nonrelativistic spin splitting. Specifically, adsorption of highly electronegative atoms (such as O and F) breaks the symmetry between opposite spin sublattices, leading to altermagnetism in $\text{VP}{X}_3$, characterized by nonrelativistic spin splitting in the band structure and a symmetry-protected zero net magnetization. In $\text{MnP}{X}_3$, adsorption of electronegative atoms induces a semiconductor-to-half metal transition, and drives an antiferromagnetic-to-ferromagnetic transition. For metal atom adsorbates (e.g., Be, Ca), their favorable configurations break all symmetries connecting opposite spin sublattices, resulting in ferrimagnetic spin splitting in $M\text{P}{X}_3$. When the system remains gapped, appropriate band filling ensures fully compensated magnetization. Our findings provide valuable guidance for designing high-performance spintronic devices based on monolayer $M\text{P}{X}_3$.