The Berry curvature dipole induced by symmetry breaking plays a pivotal role in electronic transport properties and nonlinear responses, such as the nonlinear Hall effect and circular photogalvanic effect. The study of the Berry curvature dipole is often explored in time-reversal symmetric systems, but it should not be limited to such materials. Here, we predicted that the ferroelectricity in monolayer ${\mathrm{CrNBr}}_2$ produces the Berry curvature dipole, leading to the nonlinear Hall effect and circular photogalvanic current. The linear anomalous Hall effect and circularly polarized optical absorption, governed by spin-orbit coupling, are independent of ferroelectric polarization and exhibit extremely small conductance. In contrast, multiferroic monolayer ${\mathrm{CrNBr}}_2$ achieves a large nonlinear Hall conductivity ($\sim 1e^3/\hslash \mathrm{e}{\mathrm{V}}^{-1}$ at 30 K) and circular photogalvanic current, despite its suppression at high temperatures from phonon scattering. The coupling between the ferroelectric polarization and the Berry curvature dipoles (intraband for nonlinear Hall conductance and interband for circular photogalvanic current) allows for nonvolatile switching of these effects, presenting substantial promise for nanoelectronic and optoelectronic devices.

We compute and track the impact of truly nonlocal-correlation effects on the quasiparticle (QP) band structure of hexagonal boron-nitride (h-BN) systems. To that end, we start with the consistent-exchange vdW-DF-cx version [K. Berland et al., Phys. Rev. B 89, 035412 (2014)] of the van der Waals (vdW) density functional (vdW-DF) method for exchange-correlation (XC) functional design and enforce piecewise linearity in the energy changes with partial charging, using the Koopmans-integer (KI) DFT framework [E. B. Linscott et al., J. Chem. Theory Comput. 19, 7097 (2023)]. Our approach and results, denoted KI-CX(CX) to emphasize the importance of consistency in structure and QP predictions, extends present-standard use of KI DFT, denoted KI-PBE (as it is based on the semilocal PBE XC functional but computed at the experimental structure), to capture, for example, the impact of the interlayer coupling on the QP band structure, including a full account of vdW signatures. We find that KI-CX(CX) predictions generally agree with GW studies and also with recent experimental data for bulk h-BN. We contrast QP predictions obtained in KI-CX(CX) and KI-PBE and well as in KI-PBE(PBE) (that is, KI-PBE studies based the PBE structure) and we correlate these with the core (vdW) nature of differences between the PBE and CX functionals. This analysis permits us to provide a precise discussion of what are direct and indirect vdW signatures in these layered systems and to define a new QP-based method, also denoted KI-CX(CX), for testing quality and consistency in XC functionals.

The narrow-gap semiconductor ${\mathrm{FeGa}}_3$ has attracted considerable attention due to its colossal thermoelectric Seebeck effect, intriguing magnetic anomaly, and quantum criticality. Although the quasiparticle excitations in the band gap have been probed and proposed to be directly associated with exotic characters of ${\mathrm{FeGa}}_3$, the physical origin of these in-gap states and their direct connection to either of these puzzling properties are under debate. Here, we report the discovery of the dispersive in-gap states in semiconducting ${\mathrm{FeGa}}_3$ through high-resolution angle-resolved photoemission spectroscopy. Combined with first-principles calculations and comprehensive analysis, the observed coherent in-gap states are tentatively identified as a manifestation of slightly off-stoichiometry induced ordered secondary phase, whose formula and exact lattice structure require further clarification. Notably, these dispersive in-gap states provide a consistent explanation for the exotic electronic and magnetic properties of ${\mathrm{FeGa}}_3$, establishing their origin in the previously overlooked secondary phase rather than in strong correlation effects or the trivial disorders.

Controlling collective electronic states through clean and reversible external stimuli is crucial for realizing functional quantum materials. Here, we report a study on temperature ($T$) and pressure ($P$)-tuned charge-density-wave (CDW) orders in the quasi-one-dimensional system of $\mathrm{NbS}{\mathrm{e}}_3$, through single-crystal x-ray diffraction, and electric and magnetotransport measurements. A refined and extended phase diagram is presented, prompting a reevaluation of earlier claims regarding the coexistence of CDW and superconductivity (SC). Here, SC is found to emerge only once all long-range CDWs are suppressed. Notably, the anomalous Hall and magnetoresistance (MR) effects observed at low pressure ($\mathrm{LP}\sim 0.8\mathrm{GPa}$) may arise from distinct carrier types associated with the two competing CDWs, CDW1 and CDW2. These two coexisting CDWs, characterized by distinct modulation vectors, ${\mathit{q}}_{\mathbf{1}}$ and ${\mathit{q}}_{\mathbf{2}}$, show pressure-induced opposing shifts in their $b^{*}$ axis projections (denoted as $q_1^{b*}$ and $q_2^{b*}$), while preserving a phase-coupling relationship 2(${\mathit{q}}_{\mathbf{1}}+{\mathit{q}}_{\mathbf{2}}$) $\sim \left[111\right]$. Upon gradual suppression of the long range order CDW2 order, $q_1^{b*}$ of CDW1 stabilizes and enters a decoupled regime within $\sim 0.8-1.3$ GPa, followed by a pronounced change in its periodicity between $\sim 1.3$ and 2.9 GPa. Above 2.9 GPa, all long-range CDW orders vanish, giving way to emergent superconductivity (SC).

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.