We report pressure-induced metallization in ${\mathrm{BaMn}}_2{\mathrm{P}}_2$ based on resistivity measurements in a diamond anvil cell. At ambient pressure, the temperature-dependent resistivity is well described by a two-gap Arrhenius model, yielding intrinsic and extrinsic activation energies of approximately 0.2 and 0.04 eV, respectively. Angle-resolved photoemission spectroscopy (ARPES) shows no detectable spectral weight at the Fermi level within the measured momentum window. The growth of spectral weight at higher binding energies is consistent with the energy scales inferred from transport measurements. Under pressure, the temperature dependence of the resistivity evolves from insulatinglike to mixed-slope behavior and becomes metallic above $P_c\approx 7\mathrm{GPa}$, with no low-temperature upturn. The resistivity ratio $R\left(P\right)=\rho \left(100\mathrm{K}\right)/\rho \left(300\mathrm{K}\right)$ also drops abruptly near $P_c$. A baseline transport model combining Bloch-Grüneisen phonon scattering with a thermally activated carrier density fails to reproduce this sharp change for any smoothly varying activation energy. Temperature- and pressure-dependent x-ray diffraction shows smooth evolution of $V$ with no symmetry change and no resolvable discontinuity at $P_c$. Taken together, these results indicate an abrupt pressure-driven metallization near $P_c$, with no evidence for a structural phase transition within our experimental resolution.

The Gross-Neveu model in $(2+1)$ dimensions exhibits a continuous transition from gapless Dirac semimetal to the gapped quantum anomalous Hall (QAH) insulator at a finite (attractive) coupling, at which the inversion and time-reversal symmetry become spontaneously broken, and the flavor $\mathrm{O}\left(M\right)$ symmetry remains preserved. A unification of leading-order parameters of $(2+1)$-dimensional $N$ four-component Dirac fermions collects all Lorentz-singlet masslike fermion bilinears, except the one condensing in the QAH state, into an irreducible representation of the $\mathrm{O}(M=4N)$ and predicts another phase transition in the Gross-Neveu model to occur at a strong (repulsive) coupling. Here, a fermionic auxiliary-field quantum Monte Carlo algorithm is employed in order to study a lattice realization of the Gross-Neveu field theory in the repulsive regime, where the sign problem is absent. We indeed find the $\mathrm{O}\left(4N\right)$ symmetry-breaking transition out of Dirac semimetal to occur and to be weakly first order for $N=2$, relevant to graphene. The size of the discontinuity and the magnitude of the critical coupling, however, both grow with $N$. Adding a finite chemical potential is found to break the symmetry and cause superconductivity. These results are in broad agreement with the predictions of the unified field theory. Our lattice model also displays an interesting exact $\mathrm{O}\left(2N\right)$ symmetry, a subgroup of the low-energy $\mathrm{O}\left(4N\right)$, and has the ordered ground state with the order parameter that belongs to its $N(2N-1)$-dimensional representation. Other order parameters are also examined and a certain hierarchy among those that belong to different representations of the exact $\text{O}\left(2N\right)$ is observed.

The role of collective longitudinal modes, plasmons, in bulk hydrodynamic transport in Weyl semimetals is explored. In contrast to graphene, in which these modes are gapless, plasmons in Weyl semimetals are gapped. This gap, however, can be made arbitrarily small by decreasing the temperature or the chemical potential, making plasmon modes thermally accessible in both thermodynamics and transport. In very clean Weyl semimetals near charge neutrality, where the plasmon gap is minimal, we find that they leave an imprint in the thermal conductivity and the viscosity.

We report ${}^{59}\mathrm{Co}$ and ${}^{71}\mathrm{Ga}$ nuclear magnetic resonance investigations of the quasi-one-dimensional Kondo lattice compound ${\mathrm{CeCo}}_2{\mathrm{Ga}}_8$. Below the coherence temperature, $T^{*}\approx 29\mathrm{K}$, the Knight shift, as well as the nuclear spin-spin relaxation rate, the nuclear spin-lattice relaxation rate exhibits anomalous temperature-dependent behaviors. The universal scaling of the Knight shift anomaly with temperature is in accordance with the predictions of the two-fluid model. Unlike many other heavy fermion materials, the spin-lattice relaxation rate shows a broad minimum around $T^{*}$, precisely concurrent with a rapid increase in the spin-spin relaxation rate below $T^{*}$. Our analysis suggests an enhancement of the antiferromagnetic correlation length or time below $T^{*}$, which might contribute to the emergence of heavy-electron behavior.

We theoretically investigate spin- and valley-polarized transport in planar heterostructures of transition metal dichalcogenides under modulations of off-resonant circularly polarized light, magnetic exchange fields, and gate voltage. We find that the antiferromagnetic exchange field can not only modulate different spin states, which resembles the role played by the ferromagnetic exchange field, but also dramatically change the effective band gap of a specific spin state, enabling the generation of spin polarization over a wider energy range. Off-resonant circularly polarized light tunes different valley states and the effective gap of a specific valley state, thereby generating a wide energy range for valley polarization. In the presence of both the antiferromagnetic exchange field and off-resonant circularly polarized light, the intrinsic band offset of the planar heterostructure and the external gate voltage can further tune the effective band structure, thereby tailoring the Fermi energy window for perfect spin and valley polarizations. Antiferromagnetic modulation and off-resonant circularly polarized light effectively change the band gap of different valley and spin states, making it possible for planar heterostructures of two-dimensional materials to be further applied to spintronic devices, valleytronic devices, and spin-valley filtering.

We investigate the emergence of charge waves and their temporal dynamics in one-dimensional Su-Schrieffer-Heeger (SSH) topological chains. Contrary to the conventional view that charge oscillations are suppressed in gapped topological systems with preserved chiral symmetry, we show that such oscillations can indeed occur. The general condition for an arbitrary oscillation period is analyzed, and we find that the charge waves propagating along the chain do not depend on its topology, except at the edges, where both topological phases exhibit essential differences. In chains with inequivalent atoms within the SSH unit cell, we observe regular long-period sublattice oscillations that appear simultaneously with even-odd charge oscillations. Furthermore, we study the nonequilibrium time dynamics in SSH chains. After a quench, the time evolution of the local density of states and charge occupancies exhibit clear dynamical fingerprints of the underlying topological phases. Our results demonstrate that transient charge dynamics can distinguish topologically trivial and nontrivial phases in real time by detecting the presence of topologically protected edge states.

Conjugate metamaterials (CMs), whose permittivity and permeability are complex conjugates in phase, realize simultaneous lasing and antilasing modes through a physical mechanism distinct from the conventional parity-time-symmetric framework yet limited to a special phase factor. Here, we propose a general scheme to achieve the coexistence of lasing and antilasing modes in multilayered CMs with arbitrary phase factors. By analyzing the scattering properties of cascaded CMs, the general conditions for coexistence singularities are revealed, arising from the combined effects of propagation phase resonance in each CM layer and impedance matching at the interfaces between adjacent CMs. Owing to the inherent requirement that the total accumulation of phase factors across the multilayer CMs equal odd multiples of $\pi /2$, the CM phase factor can be effectively tuned by adjusting the number of CM layers. A multilayer design consisting of a single CM and air is further proposed to realize the coexistence of lasing and antilasing modes. We design and numerically simulate the multilayer CM structure with non-Hermitian photonic crystals, successfully demonstrating controllable switching between lasing and antilasing modes. Our work provides a versatile platform for exploring non-Hermitian effects and designing multifunctional photonic devices.

Second harmonic scattering (SHS) has emerged as a powerful tool for probing molecular organization and interfacial structures in aqueous systems. Owing to its intrinsic surface sensitivity and ability to operate under in situ conditions, SHS provides valuable insights into molecular adsorption, orientation, and dynamics at interfaces that are inaccessible to linear optical methods. However, the development of SHS research faces several fundamental and technical challenges owing greatly to the discrepancy between experimental results and the approximations which interpret them stemming from unintuitive coordinate system transformations. Here, we present a reformulation of the Rayleigh-Gans-Debye approximation which defines the scattered light volume in the in-plane and out-of-plane directions to improve experiment and theory cohesion and overcome experimental challenges. These definitions are then applied to slit- and pinhole-based SHS patterns with 1° resolution and allow the complete interpretation of data from both systems. By using a slit-based collection arm nonlinear scattering experiments can integrate more of the scattered volume and increase detection sensitivity. Thorough analysis of SHS patterns from aqueous suspensions of 200 and 509 nm diameter spheres shows robust alignment with the reformulated approximation, allowing accurate prediction of polarization-resolved scattering patterns as well as geometric and polarization intensity ratios. By collecting the scattered signal over a greater collection angle, researchers will be able to retain angular resolution for the determination of scatterer geometry and molecular orientation, while improved signal-to-noise ratios will allow for enhanced simultaneous probing of interfacial identification, kinetics, and thermodynamics. Last, this work provides an approachable definition for the complete scattered light volume, which will inspire the integration of variable collection angle resolution to increase the available information in nonlinear scattering experiments into three-dimensional scattering pattern extraction.

Twisted heterobilayers of transition metal dichalcogenides exhibit a moiré pattern that translates into a honeycomb lattice of single-particle gap minima, thus resulting in a superlattice potential for excitons. The quasiparticle associated with the Bloch state of such excitons is known as a moiré exciton, and its band structure corresponds to that of a massive Dirac fermion. Here, we investigate the wavepacket dynamics of such moiré excitons using a momentum-space tight-binding model. Our results demonstrate that wavepackets that populate all the regions of gap minima at the $\mathrm{\Gamma }$-point of the moiré superlattice exhibit an elliptical, cyclotron-like motion, even for zero exciton momentum and in the absence of external forces and/or fields. We show that the period and size of these orbits are controllable via external parameters, such as perpendicularly applied electric fields and the interlayer twist angle. To provide a deeper physical insight, we derive an effective continuum model for the moiré exciton, which reveals a direct analogy to an anisotropic Rashba-like Hamiltonian, thereby explaining the origin of the elliptical trajectories. The analytical solutions for the center-of-mass motion, obtained from the Heisenberg equations of motion, are in excellent agreement with our full numerical simulations. Furthermore, we explore the topological aspects of the system, demonstrating that the anisotropic Berry curvature and the associated nonzero Chern numbers govern the directionality (clockwise or counterclockwise) of the cyclotron-like orbits, linking the exciton's trajectory to the underlying topology of its band structure.

We investigate the sine model, a one-dimensional tight-binding Hamiltonian with position-dependent sinusoidal hopping, and demonstrate the formation of synthetic horizons where electronic wave packets exhibit exponential slowdown. Interestingly, using the exact transformation between this model and the Harper equation, we find that analogous semiclassical horizons can emerge in a quantum Hall setup within the Harper-equation representation and at half filling for specific values of the magnetic flux. The Harper equation describes the eigenstates of a square-lattice tight-binding model subjected to a perpendicular magnetic field, as a family of one-dimensional problems parametrized by a conserved transverse quasimomentum. We demonstrate the correspondence between the sine and Harper models by comparing their semiclassical phase-space portraits and by numerically studying wave-packet dynamics in both models. Furthermore, by applying sudden quenches to the sine model's hopping profile, we observe the emergence of states with an effective thermal Fermi-Dirac distribution characterized by a corresponding Unruh temperature. Our numerical calculations reveal a nonuniversal behavior of this temperature, suggesting the involvement of mechanisms beyond a simple low-energy description.

We study the current-induced magneto-optical Kerr effect (MOKE) in ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ semimetalic alloys. The MOKE signal is found to be the largest in pure Bi ($x=0$), exceeding that of transition metals by nearly four orders of magnitude, and decreases monotonically with increasing Sb concentration. We find the MOKE signal scales with the resistivity ($\rho$) as ${\rho }^{1.7\pm 0.6}$ and with the mobility (${\mu }_{\mathrm{c}}$) as ${\mu }_{\mathrm{c}}^{2.0\pm 0.2}$. Model calculations show that such exponents can be accounted for if the Dirac electrons are responsible for the generation of spin current. This is in contrast to the ${\rho }^2$ and ${\mu }_{\mathrm{c}}^{-2}$ scaling of the MOKE signal induced by the free electrons in a parabolic band. The scaling of the MOKE amplitude with the resistivity also partly accounts for the order of magnitude differences of the signal observed between metals, semimetals, and semiconductors. These results demonstrate that current induced MOKE serves as an effective means to characterize the nature of spin current in materials with diverse electronic structures.

Current-driven motion of domain walls and skyrmions is central to the operation of nonvolatile magnetic memory devices. Racetrack memory requires current densities high enough to generate velocities above 50 m/s, but such conditions also enhance spin-current noise. We develop a theoretical framework based on the stochastic Thiele equation to analyze the effects of equilibrium (thermal) and nonequilibrium (spin-current) fluctuations on skyrmion dynamics. From this approach, we derive diffusion coefficients and mean-squared displacements that quantify stochastic motion under both noise sources. Micromagnetic simulations and analytical results demonstrate that spin-current noise dominates skyrmion dynamics in typical racetrack structures up to room temperature. We further address the first-passage-time problem, obtaining the mean first-passage time and its standard deviation along and across the racetrack. These results quantify how random displacements affect skyrmion propagation and detection, providing insights into error sources in high-speed racetrack memory devices.

The nature and mechanisms of dynamic deformation of two-sublattice magnetic skyrmions driven by spin-orbit torque are studied as a function of sublattice compensation using a combination of atomistic modeling and phenomenological analysis. We systematically analyze the relationship between physical distortions of the skyrmion profiles, based on the action of local Thiele forces, and internal elastic tension forces. We identify the relation between exchange-driven spin dynamics and the dynamic distortions from oppositely oriented gyrotropic forces and observe that sublattice shearing gives rise to a finite dynamical magnetization from local noncollinearity. This magnetization leads to the emergence of a local distorting force in the traveling skyrmion frame. This work provides a unifying understanding of the dynamic deformations and destabilization mechanisms that have been observed in antiferromagnetic and ferromagnetic skyrmions and had been attributed to qualitatively different mechanisms. The results will help guide material optimization for maximizing skyrmion speed and stability through informed materials selection.

Graphene provides a canonical setting for Floquet band engineering, where circularly polarized light can dynamically open topological gaps at Dirac points and generate nonequilibrium Hall responses. Here we show that uniaxial strain and off-resonant circularly polarized light with tunable incidence angle enable a controllable route to Floquet higher-order topology in graphene. Using a strained honeycomb tight-binding model with Peierls coupling and a high-frequency expansion for the effective Floquet Hamiltonian, we find that strain drives the Dirac cones toward the Dirac-merging (semi-Dirac) critical regime, where the light-induced mass becomes strongly anisotropic. For oblique incidence, the projected drive is effectively elliptically polarized and, in combination with strain, stabilizes a phase with gapped edges but robust in-gap corner modes in finite geometries, realizing a Floquet second-order topological insulator. We characterize the phase diagram via the Chern number and a crystalline-symmetry-quantized polarization invariant. Finally, first-principles-informed tight-binding calculations corroborate the predicted topological evolution in strained graphene nanostructures. Our results identify driven strained graphene as a realistic and tunable platform for realizing and diagnosing Floquet higher-order topological phases.

Recent experiments have reported valley gauge symmetry broken phases, identified as intervalley coherent (IVC) states. Exploration of anomalous responses, particularly those analogous to superconductivity, has become an urgent theoretical issue. In this study, we show that the IVC order gives rise to anomalous valley current generation driven by surface acoustic waves (SAWs). The anomalous valley current exhibits a characteristic power-law dependence for low-frequency SAWs. Furthermore, we demonstrate by numerical analysis that the IVC order leads to huge valley current generations in rhombohedral graphene. These results open a pathway toward exploring exotic phenomena emerging from valley gauge symmetry breaking, in close analogy with gauge symmetry breaking in superconductors.

Accurate characterization of thermodynamic phases and domain structures is crucial for the engineering of polar-textured thin-film electronic devices. In an improvement to the phase prediction, a Landau-Ginzburg-Devonshire thermodynamic model of ferroic materials is extended to generalized elastic and electromagnetic boundary conditions. The proposed mathematical framework allows for the implementation of a modular computational model which can analyze composite systems with solid solutions, multiple material layers, and domain structures. The model is applied to epitaxially constrained solid solutions of barium and strontium titanates, with the results illustrating the similarity in the evolution of the single-domain and polydomain ferroelectric phases across a wide range of material compositions. In the applications where barium titanate is placed near a phase boundary, further refinement of the characterization of the boundary can be achieved with the inclusion of the inequality of domain sizes and the tilting of the domain wall within the computational model.