We study the collective modes in a noncentrosymmetric superconductor with Rashba spin-orbit coupling under laser irradiation. The concept of Anderson Pseudospin Resonance allows us to reveal how laser driving gives rise not only to the established resonant enhancement of third harmonic response, but also to a resonant enhancement in the second-harmonic response of the spin current. We propose a theory that explains the phenomenon without including interband transitions. The theory is corroborated by numerical simulations, which incorporate interband effects and allow us to clarify the signatures of the collective modes in the long-time dynamics of the superconductor.

Spontaneous time-reversal symmetry breaking in superconductors with competing nondegenerate pairing channels is an exotic quantum phase transition that could give rise to robust topological superconductivity and unusual magnetism. It is proposed mostly in two-dimensional systems and is signaled by a nonzero relative phase between the two superconducting order parameters, hence it should particularly be prone to order-parameter phase fluctuations. Nevertheless, the existing understanding of it is still at the mean-field level. Here, we illustrate the non-negligible effects of the phase fluctuations on such quantum phase transitions using the hole-doped square-lattice $t-J$ model as an example. We derive the phase fluctuation-corrected free energy and show that under the quantum phase fluctuations, the time-reversal asymmetric $s+\mathrm{i}d$ phase region splits off a dome featuring a first-order border with the $d$ phase, indicating the possibility of a phase separation into the time-reversal symmetric and asymmetric phases. The phase fluctuations also narrow the range of the $s+\mathrm{i}d$ phase considerably. We further discuss the implications of our findings for recent experiments on disorder-induced first-order quantum breakdown of superconductivity and promising high-temperature topological superconductivity in twisted cuprate Josephson junctions.

Accurate pressure calibration is fundamental to quantitative high-pressure science, yet inconsistencies among widely used secondary pressure scales persist. We report simultaneous synchrotron x-ray diffraction measurements on nine common pressure calibrants (Pt, Cu, Au, Mo, Ta, W, Fe, MgO, and NaCl) compressed together in diamond anvil cells to 140 GPa. This simultaneous-measurement strategy minimizes transitive errors and run-to-run inconsistencies inherent to paired-measurement approaches, yielding direct experimental volume-volume (V-V) relations among the calibrants. These V-V relations link the compression state of each phase to that of every other phase measured in the same experiment. By anchoring these V-V relations to the reduced 300 K equation of state (EOS) of copper derived from ramp-compression measurements, we derive an internally consistent set of Cu-referenced pressure scales via Vinet EOS fits. Because the primary experimental result is the V-V dataset, it provides an EOS-independent constraint that can be rereferenced if primary standards are revised. The dataset further enables a direct experimental cross-check of consistency between the adopted reduced 300 K Cu EOS and the corresponding reduced 300 K ramp-derived EOSs for Pt, Au, Ta, and hcp-Fe under a fixed V-V constraint. The residuals quantify small, material-dependent mismatches between each phase EOS and the Cu reference EOS.

Periodic boundary conditions are not always used in the study of disordered systems, but it can be advantageous to apply them to mimick thermodynamically large systems. In this case, polarization and its cumulants cannot be obtained directly but through the tools of the modern theory of polarization. This theory casts the polarization in crystalline systems as a geometric phase rather than an operator expectation value. We develop disorder averaging techniques within the context of this theory which can calculate the variance of the polarization, its higher-order moments, and the excess kurtosis (or Binder cumulant). We also derive an indicator of delocalization based on the degeneracy as a function of boundary conditions. We apply the computational techniques to two model systems. To test localization, we use a one-dimensional disordered model which is fully Anderson localized. Our calculations verify this. We also apply our techniques to the one-dimensional de Moura-Lyra model, developed to study power-law correlated (controlled by a parameter, $\alpha$) disorder. While this model is a pathological one, our method is validated. We also point out the significance of pairwise degeneracies found in the parameter range, $\alpha >2$, and near the band center (or near half filling), where the model was conjectured to exhibit a mobility edge.

Rare-earth monopnictides offer a unique testbed for exploring the entanglement of localized $4f$ moments with itinerant electrons. In this family, TbBi occupies a distinctive yet poorly understood position, characterized by intermediate magnetic anisotropy and a borderline topological electronic structure. In this paper, we combine magnetic and magnetotransport studies on TbBi single crystals to reveal how the moderate anisotropy governs both its magnetic phase diagram and charge conduction. We identify a field-induced spin-flop transition in the antiferromagnetic state that leaves a clear imprint on the bulk transport—most notably as a pronounced concave curvature in the isothermal magnetoresistance, a signature seldomly observed in rare-earth monopnictides. Angular magnetoresistance measurements further serve as a phase-sensitive probe: At low (∼2 K) or high (>10 K) temperatures, the response is governed by Fermi-surface anisotropy, resembling a nonmagnetic system. However, in a critical temperature window (2–10 K), additional extrema emerge that track the field- and angle-induced reorientation of the antiferromagnetic order from FeO-type phase to a spin-flop state, and vice versa. Our work not only fills a critical gap in understanding correlated phenomena in rare-earth monopnictides but also establishes TbBi as a key material for investigating spin-flop-driven anomalies in transport at the intersection of magnetic and topological phases.

We study an extended Kitaev model on the triangular lattice in a limit where the symmetric off-diagonal bond-dependent and Heisenberg interactions together map onto an XXZ model, in addition to the Kitaev interaction. Within the previously identified ${\mathbb{Z}}_2$ vortex regime, we uncover a ferrichiral skyrmion phase characterized by a sublattice-resolved scalar chirality: two of the three sublattices carry unit skyrmion charge, while the third remains nonchiral. Using classical Monte Carlo simulations, we show that this ferrichiral skyrmion phase emerges at zero temperature and in the absence of both an external magnetic field and Dzyaloshinskii-Moriya interactions, in sharp contrast to conventional skyrmion-hosting systems. The phase is stable over a wide parameter window and persists to relatively high temperatures. Our results reveal an unconventional route to skyrmion physics driven purely by frustrated exchange interactions and highlight the emergence of rich topological structures. Since both XXZ anisotropy and Kitaev interactions originate from the same spin-orbit-coupling mechanism, materials traditionally classified as XXZ magnets are expected to host finite Kitaev interactions as well. The potential for ferrichirality in these systems therefore warrants further investigation.

We investigate an $S=3/2$ quantum spin model on a two-dimensional honeycomb lattice that continuously interpolates between two paradigmatic quantum disordered states with distinct entanglement structures: the Kitaev quantum spin liquid and the Affleck-Kennedy-Lieb-Tasaki (AKLT) valence bond solid. Combining classical, semiclassical, and exact diagonalization approaches, we map out the ground-state phase diagram and elucidate the role of quantum fluctuations across the entire parameter range. While classical and semiclassical frameworks predict noncoplanar orders competing with a collinear Néel state, we find these phases to be fragile: once full quantum fluctuations are included, they melt into a quantum-entangled state characterized by suppressed spin correlations and enhanced entanglement entropy. Our findings highlight how competition between qualitatively different quantum disordered phases provides a fertile playground for unconventional phases emerging from their interplay and quantum fluctuations.

We study how an out-of-plane magnetic field $B\left(\mathbf{r}\right)$ and a Berry curvature $\mathrm{\Omega }\left(\mathbf{k}\right)$ modify the exchange interactions in a two-dimensional Wigner crystal (WC) using a semiclassical large-$r_s$ expansion. When only a magnetic field is present, ring-exchange processes arise from multiparticle tunneling through complex trajectories which constitute complex instanton solutions of the coordinate-space path integral. To leading order in $B$, each exchange constant $J_a$ acquires an Aharonov-Bohm phase along the zero-field tunneling trajectory. When a Berry curvature is present, the multiparticle tunneling must be considered in a complexified phase space $(\mathbf{r},\mathbf{k})$. To leading order in $\mathrm{\Omega }, J_a$ acquires a Berry phase along a purely imaginary momentum-space trajectory. When $B$ and $\mathrm{\Omega }$ are both present, in addition to having both Aharonov-Bohm and Berry phases, the exchange magnitude $|J_a|$ is also exponentially modified due to an effective-mass renormalization. These effects could be relevant for the WC and proximate phases recently observed in rhombohedral multilayer graphene.

We present a systematic study of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ films under both dark and illuminated conditions. In the dark, the intrinsic magnetism of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is shown to yield a stronger anisotropic RKKY spin model compared to nonmagnetic topological insulators, providing a clear signature for differentiating these systems. Furthermore, key band properties—such as energy gap, band degeneracy/splitting, and topological deformations of the Fermi surface—imprint distinct signatures on the RKKY interaction, enabling clear discrimination between axion insulators (AI) and quantum anomalous Hall (QAH) insulators in even- and odd-septuple-layer (SL) films. This discrimination manifests in multiple ways: through the Fermi-energy dependence or spatial oscillations of the interaction for impurities on the same surface, or via the presence versus absence of spin-frustrated terms for those on different surfaces. Under off-resonant circularly polarized light, additional phase-transition-related fingerprints also emerge to distinguish these two phases, such as sign reversals of spin-frustrated terms in even-SL films versus chirality-selective double-dip structures of collinear RKKY components in odd-SL films. Overall, this work establishes RKKY interactions as a sensitive magnetic probe for distinguishing between AI phase (even-SL) and QAH phase (odd-SL), thereby complementing conventional electrical measurements while providing new insights into the influence of intrinsic magnetism on the surface-state band structure.

Mean-field one-dimensional topological superconductors host edge Majorana zero modes (MZMs) that encode a topologically protected ground-state degeneracy and enable robust braiding operations within this subspace. Mean-field states lack definite particle number and thus cannot represent isolated systems. Nevertheless, projecting them onto fixed particle number can yield good approximations to an isolated superconductor ground state. In earlier work [Sajith et al., Phys. Rev. B 109, 184509 (2024)] we showed that the projected Kitaev wave function of a single wire preserves some important mean-field features, such as the zero-energy spectral peaks near the wire edges. However, uniqueness of the fixed-number ground state does not allow for any nontrivial operations in the ground-state subspace. To overcome this limitation, here we consider the case of multiple wires with a conserved total charge, using the same approach. In the limit of vanishing interwire coupling, this system has a macroscopic ground-state degeneracy. We show how this degeneracy is resolved by coherent single-particle tunneling, and identify special many-body states which play the same role as the MZM parity states in the mean field. We demonstrate how braiding operations can be implemented and discuss both intrinsic and extrinsic limits on their fidelity.

We theoretically investigate the spin structure and spin dynamics of excitons in bulk lead halide perovskite semiconductors with cubic, tetragonal, and orthorhombic crystal symmetry. The exciton spin structure and its modification by an external magnetic field are modeled for different regimes defined by the relative magnitude of the electron–hole exchange interaction (splitting between dark and bright states) and the Zeeman spin splitting. The effects of crystal symmetry and magnetic field orientation with respect to the crystal axes are considered for lead halide perovskite crystals with band gaps in the range of 1.4 to 3.5 eV, having different ratios of electron and hole $g$-factors. For cubic symmetry, in a longitudinal magnetic field, our theory predicts quantum beats between the bright exciton states under linearly polarized excitation and detection, while the dark exciton remains optically inactive. In a transverse magnetic field, all exciton spin states become optically active and can be excited by circularly polarized light. Reduction of the crystal symmetry leads to a zero-field offset of the exciton Larmor precession frequencies, modifying the Zeeman splitting energy dependence on magnetic field. This theoretical framework allows for the extraction of the strength of the exchange interaction and the crystal symmetry. Experimentally, we measure the exciton spin coherence via time-resolved photoluminescence at a temperature of 1.6 K in longitudinal and transverse magnetic fields in orthorhombic ${\mathrm{MAPbI}}_3$ crystals. Polarization beats at the frequency of the bright exciton are observed in both configurations. Comparison with theory indicates that the excitons are in the strong exchange interaction regime, and the reduction of symmetry does not lead to a significant splitting of the exciton spin levels.

Flat bands in moiré lattices of transition-metal dichalcogenides have emerged as a powerful platform for exploring strongly correlated electron physics. However, the moiré flat bands in these systems caused by band folding can originate from different valleys, which complicates the physics of the flat bands. Here, we combine a band-unfolding technique with symmetry analysis to visualize how the $\mathrm{\Gamma }$ valley gives rise to flat bands for the $R$- and $H$-stacking moiré superlattices of the homobilayers. We demonstrate that the $\mathrm{\Gamma }$ valley—at the center of the Brillouin zone—interacts with its folded bands under the effect of moiré potential, then forms flat bands as the twist angle decreases. Furthermore, the topmost two $\mathrm{\Gamma }$ flat bands in $R$-stacking moiré systems maintain a robust Dirac node at the K point protected by $D_3$ symmetry. In contrast, the $\mathrm{\Gamma }$ flat bands open a gap at K in the $H$-stacking moiré superlattices due to having a $C_3$ symmetry. As a result, the change from the $R$-stacking order to the $H$-stacking order in the moiré systems causes the $\mathrm{\Gamma }$ flat bands to transform from a honeycomb lattice to a triangular lattice. The K-valley flat bands for both types of moiré superlattices exhibit similar dispersion features.

The Hubbard model on the kagome lattice is a widely used interacting model for describing the electronic properties of various transition-metal-based kagome materials. We find altermagnetism driven by Coulomb interaction in the kagome Hubbard model at Dirac filling with no spin-orbit coupling nor explicit spatial symmetry breaking present. We show how this insulating altermagnet is relevant to other lattices with larger unit cells such as the Lieb-kagome lattice. The altermagnet found displays a characteristic magnon splitting, which can be detected in inelastic neutron scattering experiments on interacting kagome materials.

In isolated quantum many-body systems periodically driven in time, the asymptotic dynamics at late times can exhibit distinct behavior such as thermalization or dynamical freezing. Understanding the properties of and the convergence towards infinite-time (nonequilibrium) steady states, however, remains a challenging endeavor. We propose a physically motivated Krylov space perspective on Floquet thermalization which offers a natural framework to study rates of convergence towards steady states and, simultaneously, an efficient numerical algorithm to evaluate infinite-time averages of observables within the diagonal ensemble. The effectiveness of our algorithm is demonstrated by applying it to the periodically driven mixed-field Ising model, reaching system sizes of up to 30 spins. Our method successfully resolves the transition between the ergodic and dynamically frozen phases and provides insight into the nature of the Floquet eigenstates across the phase diagram. Furthermore, we show that the long-time behavior is encoded within the localization properties of the Ritz vectors under the Floquet evolution, providing an accurate diagnostic of ergodicity.

We develop a Monte Carlo sampling algorithm to numerically evaluate the Lehmann representation for the finite temperature single-particle Green's function in the repulsive Lieb-Liniger model. This allows us to determine the spectral function in the full range of temperatures and interactions, as well as in generalized Gibbs ensembles. We test our results against known results for dynamics at infinite interaction strength and static correlators, and find excellent agreement.

Rabi oscillations characterize light-matter hybridization in the waveguide quantum electrodynamics (WQED) framework, with their associated decay rates reflecting excitation damping, yet their behavior remains unresolved when collective emitters are coupled to a collective waveguide mode. This scenario reveals a conceptually novel collective-light-collective-matter interaction, realizable when a timed-Dicke state of subwavelength emitters couples to a slow, delocalized surface-plasmon mode, forming a hybridized plasmon-polariton (HPP). The HPP acquires its directionality from the timed-Dicke state via momentum matching. It also exhibits plasmonic characteristics, with excitation frequencies following the surface-plasmon dispersion relation. We obtain a Rabi oscillation and a long-time decay that describe the HPP and use them to reveal weak- and strong-coupling regimes through the emergence of normal-mode splitting. By performing a finite-time Lyapunov-exponent analysis, we show that the HPP also exhibits instantaneous decay and numerically identify three distinct decay regimes: early-time rapid, transient-time oscillatory, and long-time classical. Finally, by analyzing the emission spectrum, we observe an anticrossing of the peak doublets—a feature also seen in cavity quantum electrodynamics setups—which originates from quantum vacuum effects and the resulting non-Markovian HPP evolution in our WQED.

We consider the excitation of Higgs modes via the modulation of the Bardeen-Cooper-Schrieffer coupling within the Migdal-Eliashberg-Keldysh theory of time-dependent superconductivity. Despite the presence of phonons, which break integrability, we observe Higgs amplitude oscillations reminiscent of the integrable case. The dynamics of quasiparticles follows from the effective Bogolyubov–de Gennes (BdG) equations, which represent a Floquet problem for the Bogolyubov quasiparticles. We find that when the Floquet-Bogolyubov bands overlap, the homogeneous solution formally leads to a negative superfluid density, which is no longer proportional to the amplitude of the order parameter. This result indicates an instability, which we explore using spatially resolved BdG equations. Spontaneous appearance of spatial inhomogeneities in the order parameter is observed and they first occur when the superfluid density becomes unphysical. We conclude that the homogeneous solution to time-dependent superconductivity is generally unstable and breaks up into a complicated spatial landscape via an avalanche of topological excitations.

Using a self-consistent Hartree-Fock theory, we show that the recently observed ferromagnetism in twisted bilayer ${\mathrm{WSe}}_2$ [Nat. Commun. 16, 1959 (2025)] can be understood as a Stoner-like instability of interaction-renormalized moiré bands. We quantitatively reproduce the observed Lifshitz transition as function of hole filling and applied electric field that marks the boundary between layer-hybridized and layer-polarized regimes. The former supports a ferromagnetic valley-polarized ground state below half-filling, developing a topological charge gap at half-filling for smaller twist angles. At larger twist angles, the system hosts a gapped triangular Néel antiferromagnet. On the other hand, the layer-polarized regime supports a stripe antiferromagnet below half-filling and a wing-shaped multiferroic ground state above half-filling. We map the evolution of these states as a function of filling factor, electric field, twist angle, and interaction strength. Our results demonstrate that long-range exchange in a symmetry-unbroken parent state with strongly renormalized moiré bands provides a broadly applicable framework to understand itinerant magnetism in moiré TMDs.

Vortex waves carrying quantized orbital angular momentum (OAM) have been extensively studied in optical and acoustic systems, yet their realization in fully vectorial elastic media is generally hindered by intrinsic longitudinal-transverse coupling. Here, we introduce a cut-and-glue topological lattice defect (TLD) in a three-dimensional elastic Weyl phononic crystal and realize a defect-bound mode propagating along the defect line with a vortex phase structure. The TLD preserves axial translational symmetry, giving rise to a one-dimensional defect band dispersing with ${\mathit{k}}_{\mathit{z}}$ that topologically connects a pair of Weyl points with opposite chirality in momentum space. The resulting defect-bound mode is strongly localized at the defect core, carries a well-defined OAM with winding number $\ell =1$, and maintains longitudinal-dominant polarization across the entire defect band. These findings establish a bulk-defect topological mechanism for robust OAM-guided transport in fully vectorial three-dimensional elastic media.

Bound states in the continuum (BICs) have emerged as a powerful platform for enhancing wave-matter interactions, owing to their ultrahigh quality ($Q$) factors arising from extreme energy localization. While symmetry breaking in BIC-based metasurfaces can yield strong chiral responses, most existing studies have focused on single BIC systems, leaving their coupling and interactions largely unexplored. In this work, we propose a coupling-induced chiral quasi-BIC (QBIC) in an acoustic system. By introducing a coupling channel between a pair of BICs, perfect vortex patterns are observed in the far-field radiation at both ends, where the chiral responses are independently tunable for each port and maintain robustness against parameter perturbations. In a scattering network, the designed chiral QBIC exhibits maximum chirality-selective transmission for acoustic vortices, which is validated by an experimental prototype. Additionally, an exceptional line emerges in the parameter space of the scattering matrix as a non-Hermitian feature, revealing the origin of robust chirality and enabling tunability of the $Q$ factor. Our work provides an efficient way for chirality manipulation using BICs and may enrich the understanding of wave physics.