We investigate localization in a one-dimensional non-Hermitian Aubry-André model in which both the nearest-neighbor and the next-nearest-neighbor hoppings are nonreciprocal. Combining the Fermi-surface point-matching approximation with an effective-hopping ansatz that is exact in the two solvable limits of the model, we obtain an approximate closed-form mobility edge in which the two nonreciprocity parameters enter through exponentially renormalized hopping amplitudes. In the Hermitian limit, the real-to-complex transition of the eigenvalues under a weak imaginary vector potential locates the mobility edge sharply and shows that the point-matching expression is more accurate than an earlier approximate expression obtained by mapping to a model with exponentially decaying hopping. For nonreciprocities of equal sign, the mobility edge is a parabola in the energy-potential plane: nearest-neighbor nonreciprocity shifts it toward stronger potentials, whereas next-nearest-neighbor nonreciprocity reduces its curvature and widens the window in which extended and localized states coexist. Exact diagonalization and global phase diagrams confirm this picture and delimit the range of validity of the approximation. Spectral winding numbers evaluated near the two band edges bracket the mixed phase.

Color defect centers carrying electron spins in solid crystals such as diamond and silicon carbide (SiC) are promising candidates for qubits and quantum sensors, with SiC material being particularly interesting due to its compatibility with the existing semiconductor technology. Here we investigated the electron spin properties of silicon vacancy centers (V1 and V2), both having electron spin $S=3/2$ in $4H\text{−}\mathrm{SiC}$ in the temperature range $T=80–300\mathrm{K}$ using electron paramagnetic resonance (EPR). The EPR spectrum shows central and satellite lines, where the former ones originate from V1 and V2 centers, as well as from unknown defect center X. The analysis of continuous-wave EPR measurements revealed a spin concentration of $c_{\mathrm{V}1}=1.47\pm 0.3\times {10}^{14}$, $c_{\mathrm{V}2}=5.6\pm 1.12\times {10}^{13}$, and $c_{\text{X}}=1.03\pm 0.21\times {10}^{13}$ $\mathrm{spins}/{\mathrm{cm}}^3$. Additionally, electron spin coherence $T_2$ and relaxation times $T_1$ have been measured on the central and on the satellite spectral lines, resulting in longer $T_1$ and $T_2$ for the satellite transition, compared to the central one, with maximum values of $42.8\pm 1.3$ ms and $0.708\pm 0.004$ ms, respectively, at $T=80\mathrm{K}$. We reveal that decoherence is mainly caused by nuclear and electron spin diffusion.

Controlling magnetism by electric field or current is a central topic in spintronics. In this work we argue that the magnon spin photocurrent can also be controlled by the electric field in magnetoelectrics. Taking ${\mathrm{Cr}}_2{\mathrm{O}}_3$ as an example, we demonstrate how the spin current is modified by the electric field using nonlinear response theory. We find that the Dzyaloshinskii–Moriya interaction induced by the applied field plays a key role in modifying spin-current conductivity, which exhibits pronounced anisotropy with respect to the light polarization. In particular, both the resonance frequency and the peak intensity show distinct dependencies on the external electric field $E$, demonstrating electrical control of the spin photocurrent. In addition, we show that the two-magnon processes give rise to a continuum spectrum, a consequence of the field-induced spin canting. These results show that ${\mathrm{Cr}}_2{\mathrm{O}}_3$ is a promising platform for realizing electrically tunable spin photovoltaic effect.

Multiferroics with ferroelectric and altermagnetic orders have been a focus in spintronics for exploring emergent magnetoelectric coupling and electric-field controlled low-power spintronics. Using symmetry analysis and first-principles calculations, we verify that quasi-one-dimensional ${\mathrm{MoOBr}}_3$ is a ferroelectric altermagnet. Reversal of the electronic polarization preserves the band spin splitting in reciprocal space but flips the sign of the linear magnetoelectric coupling coefficient in real space, realizing a nonvolatile magnetoelectric response. Upon applying hydrostatic pressure, a structural phase transition occurs from the ferroelectric phase with parallel interchain polarizations to the antiferroelectric phase with antiparallel interchain polarizations. Taking into account spin-orbit coupling, in-plane rotation of the Néel vector drives the system into a polar magnetic point group and induces ferroelectric polarization along the chain, enabling the strong magnetically driven magnetoelectric coupling characteristic. Our findings demonstrate that the synergy between ferroelectricity and altermagnetism enables nonvolatile and switchable magnetoelectric coupling in ${\mathrm{MoOBr}}_3$, providing a potential platform for energy-efficient magnetoelectric memory and electrically controlled magnetoelectric functionalities.

We theoretically study how to design spin couplings in networks of Majorana Cooper pair boxes (MCBs) connected by multiple normal-metal leads. The interbox interaction is generated by the conduction-electron-mediated Ruderman-Kittel-Kasuya-Yosida interaction. We show that the connectivity of Majoranas to the leads enables arbitrary types of couplings. As concrete examples, we show the realization of the XY and Dzyaloshinskii-Moriya couplings, which are difficult to implement in previously proposed MCB-based schemes. The sign and magnitude of the couplings can be tuned continuously via gate-controlled tunneling amplitudes. These results establish MCBs as a versatile platform for engineered quantum spin systems.

The momentum-space signatures of excitons can be experimentally accessed through time-resolved (pump-probe) photoelectron spectroscopy. In this work, we develop a computational framework for exciton photoemission orbital tomography (exPOT) in periodic systems, enabling the simulation and interpretation of experimental observables within many-body perturbation theory. By connecting the $GW+$ Bethe-Salpeter equation (BSE) approach to photoemission tomography, our formalism captures exciton photoemission in periodic systems, explicitly incorporating photoemission matrix element effects induced by the light-matter interaction via the probe pulse. The correlated nature of electrons and holes introduces distinct consequences for excitonic photoemission. Using the prototypical two-dimensional material hexagonal boron nitride, we demonstrate these effects, including a dependence of the photoemission angular distribution on the pump pulse polarization. Moreover, our framework extends to excitons with finite center-of-mass momentum, making it well-suited to studying momentum-dark excitons. This provides valuable insights into the microscopic nature of excitonic phenomena in quantum materials.

The stoichiometric antiferromagnetic insulator ${\mathrm{EuTiO}}_3$ is proximate to a ferroelectric phase. Whereas cation substitution has been used as a tuning parameter to introduce charge carriers and manipulate the magnetism, the effects of oxygen-vacancy doping have been less explored. Here we report a detailed study of the charge transport and magnetic properties of metallic, oxygen-vacancy-doped $\mathrm{EuTi}{\mathrm{O}}_{3-\delta }$. Using ${\mathrm{CaH}}_2$ as an oxygen getter to achieve a higher carrier concentration than previously reported, we find that the phase diagram of the oxygen-vacancy-doped system is distinct from that obtained via cation doping. In particular, we uncover a change from antiferromagnetic to ferromagnetic order in the metallic state, with a maximum Curie temperature of $T_C \approx 11$ K at the highest carrier concentration of $n \approx {10}^{21}\mathrm{c}{\mathrm{m}}^{-3}$. These findings are supported by density functional theory calculations, which indicate a significant change in the nearest-neighbor magnetic exchange constant with increasing electron doping. We also present x-ray diffuse scattering and complementary first-principles results that reveal that, similar to the prominent incipient ferroelectric perovskite ${\mathrm{SrTiO}}_3$, the data for as-grown ${\mathrm{EuTiO}}_3$ are consistent with thermal diffuse scattering and with the absence of quasielastic contributions. For oxygen-vacancy-doped $\mathrm{EuTi}{\mathrm{O}}_{3-\delta }$, the x-ray data reveal a lower cubic-tetragonal transition temperature and additional short-range correlations at low temperatures. Finally, we report specific heat measurements that confirm the magnetic transition temperatures deduced from magnetization measurements and corroborate the lattice dynamics picture inferred from the diffuse scattering data.

We develop a hydrodynamic theory of charge and heat currents induced by traveling waves, such as surface acoustic waves, in graphene devices near charge neutrality. The currents depend on the intrinsic conductivity and viscosity of the electron liquid, the disorder strength, and the geometry of the device. We obtain analytic expressions for the heat and charge currents to second order in the wave amplitude for Hall-bar devices. At charge neutrality and in the absence of dc bias, the heat content is entrained by the wave in the absence of net charge transfer. At the same time, device conductance is enhanced by the wave. Away from charge neutrality, the transport charge current induced by the wave arises in the absence of a dc bias.

Non-Hermitian periodic wave systems display unusual behaviors that are not accounted for by traditional Bloch band theory, including the localization of entire bands of eigenstates near the edges of finite-size samples (the non-Hermitian skin effect). Recent theoretical work, mostly focused on discrete lattice models, has introduced the notion of a generalized Brillouin zone (GBZ) in complex reciprocal space to explain these phenomena. Here we extend this description to the case of photonic crystals, which hold great promise for the investigation of non-Hermitian effects in continuous lattices and their exploitation for practical device applications. Our approach is based on a tight-binding model that can be applied to any given photonic crystal to provide a direct and computationally efficient connection to non-Bloch band theory. As an illustration, we use this model to compute the complex frequency spectrum and GBZ of a finite two-dimensional lattice of lossy triangular building blocks. The results highlight a rich localization behavior for the skin modes and an intricate evolution of the GBZ controlled by the crystal wave vector parallel to the open boundaries. The framework developed in this work is attractive for the design and modeling of non-Hermitian photonic crystals of high structural complexity, where traditional electromagnetic simulations can become prohibitively expensive in terms of the required computational resources to handle finite-size systems. Furthermore, it introduces a powerful tool for theoretical studies where knowledge of the GBZ is required, including the investigation of topological phase transitions in photonic non-Hermitian settings.

Simulating nonequilibrium quantum many-body systems remains a major challenge due to the exponential growth of the computational complexity with real time. Here we implement a nonequilibrium impurity solver based on the weak-coupling expansion and the tensor cross interpolation, and apply it to nonequilibrium dynamical mean-field theory (DMFT). The method approximates the integrands of the high-dimensional integrals arising in the weak-coupling expansion in a tensor-train form, enabling efficient evaluations without stochastic sampling and thereby mitigating the sign problem affecting continuous-time quantum Monte Carlo (CT-QMC) methods. Benchmark calculations for an exactly solvable nonequilibrium impurity model agree well with the exact results and reveal a low-rank structure of the integrands. When applied to interaction-quench problems in the half-filled Hubbard model, the method reproduces fast thermalization at a critical interaction strength with accuracy comparable to CT-QMC. Away from half filling, where the sign problem becomes even more severe, the present approach remains well controlled, revealing a crossover instead of a sharply defined fast thermalization point in the 3/4-filled case. The solver can also be applied to steady-state DMFT problems, yielding accurate spectral functions in the metallic regime without analytic continuation.

The Seebeck coefficient quantifies the voltage generated across a material in response to a temperature gradient. Recent studies have shown that strong electronic correlations can enhance this coefficient, producing anomalous behavior near half-filling associated with the Mott plateau. This raises the possibility that other interaction scales, not necessarily originating in Mott physics, could give rise to similar enhancements. Here, we investigate the Seebeck coefficient in the presence of attractive interactions, nearest-neighbor interactions, sublattice potentials, and electron-phonon coupling. The Seebeck coefficient is obtained via the Kelvin formula, using entropy data derived from density calculations within determinant quantum Monte Carlo. We find that these additional interaction scales can indeed enhance the Seebeck coefficient and further induce multiple sign changes as a function of doping. We show that this anomalous behavior is associated with the opening of a gap in the ground state, as computed via cluster perturbation theory. Moreover, electron-phonon coupling alone, even in the absence of onsite repulsion, can produce a Seebeck anomaly. We relate these sign changes to a restructuring of the Fermi surface and an accompanying change in its topology, an effect commonly observed in cuprates.

We study phase diagrams of charge-conserving ‘‘class A’’ noninteracting fermions, focusing on the trivial phase in various dimensions. Such phases are usually termed ‘‘featureless’’ to distinguish them from those others with either symmetry-broken or topological order. We show that the presence of nontrivial topological families of states, including charge pumps and their generalizations, results in phase diagrams being endowed with nontrivial topological textures that can be visualized through Berry phases and their higher-dimensional generalizations. We show that for noninteracting fermion systems with translation invariance, these ‘‘higher’’ Berry phases can be computed using integrals of non-Abelian Chern–Simons forms of the Berry–Bloch connection over momentum and parameter spaces. Singularities in these textures correspond to gap-closing loci of ‘‘diabolical points’’, which represent the obstruction to contracting topologically nontrivial families of states, and bulk-boundary correspondence results in a locus of robust boundary modes that terminate at the bulk diabolical points. In the presence of finite chemical potential, we argue that the edge modes are generically robust without any need for fine-tuning for two and higher dimensions, whereas in one dimension they are ‘‘estranged’’ in the phase diagram, i.e., appearing at different parameter values for different edges. We demonstrate our results by constructing several microscopic models of noninteracting fermions. We argue stability to interactions and explore proximate phase diagrams by mapping to continuum field theories.

Phonon scattering by charge carriers and impurities reduces the thermal conductivity in heavily doped semiconductors, but understanding of the respective roles of these mechanisms is still lacking, as previous works arrived at apparently contradicting conclusions regarding the dominant reduction mechanism. In this work, we study the thermal conductivity of P- and B-doped silicon experimentally with the $3\omega$ method, as well as with predictive density-functional-theory-based calculations. Our work offers a generalized picture of two distinct heat-transport reduction regimes: one due to charge-carrier scattering and another due to impurity scattering, which depend on temperature, doping concentration, and the size of the heat source. We further propose a simple concentration-dependent thermal conductivity reduction model, which demonstrates that the two reduction regimes can be clearly distinguished by different exponential stretching. Our findings reconcile the claims of previous works and can be applied to other doped semiconductors.

Conventionally, the magneto-optical Faraday effect is considered as a bulk magneto-optical effect, and for the isotropic homogeneous thin films its sign is fully determined by the sign of the nondiagonal permittivity element. Here we experimentally reveal an additional contribution to the Faraday effect from the film interfaces. It becomes notable in the absorption band for films with a thickness of a few tens of nanometers. As a result, a novel feature of the Faraday effect is observed and numerically confirmed: the sign of the Faraday rotation at a fixed wavelength becomes dependent on the film thickness and therefore is ambiguously related to the sign of the gyration and magnetization of the film. We elaborated an analytical model taking into account the bulk and interfacial contributions and interference due to multiple internal reflections, which nicely reproduces the experimental data. Moreover, our joint analysis of Faraday rotation and ellipticity reveals an additional bulk contribution to the Faraday rotation: magnetic circular dichroism combined with multiple internal reflections produces a finite phase difference between the transmitted circularly polarized waves even when the conventional single-pass bulk contribution vanishes. Possible applications of the observed unusual Faraday rotation behavior include sensing as well as other devices performing polarization control at nanoscale.

Electronic many-body effects govern aqueous redox thermodynamics, yet their roles in transition metal redox chemistry remain poorly understood. Here, we systematically compare density functional theory and random phase approximation (RPA)-based methods using statistically converged first-principles free-energy calculations. We show that density functional errors correlate strongly with the self-interaction error and are substantially reduced when the straight-line condition is satisfied. In contrast, RPA-based methods exhibit substantial errors that show no clear correlation with self-interaction error. Combined analyses using beyond-RPA methods and correlated wave-function calculations show that complete second-order correlation, infinite summation of ring diagrams, renormalized single excitations, and empirically optimized functionals of the RPA response each fail, individually, to yield accurate redox levels, a trend consistently observed from isolated ions to clusters and the bulk solution, highlighting the need for balanced higher-order correlations for localized $d$-electron systems in solution.

The photoluminescence (PL) of momentum-indirect $\mathrm{\Gamma }-K$ excitons in monolayer ${\mathrm{WS}}_2$ under biaxial strain was recently observed by [Blundo et al., Phys. Rev. Lett. 129, 067402 (2022)], yet the microscopic mechanism governing their formation, optical activation, and valley response remains unresolved. Here, we establish a unified microscopic framework bridging exciton formation, population redistribution, PL, and valley polarization. We identify a previously overlooked higher-energy intermediate exciton and reveal a two-step formation mechanism: Optically generated bright excitons first transfer to this intermediate state through exchange interaction and then relax into momentum-indirect excitons via spin-flip scattering. This mechanism explains the strain-dependent PL redistribution in experiment and identifies true hybridized direct-indirect eigenbranches as the PL-active states. Beyond explaining experiment, our theory predicts a strain-driven, sign-changing “sinusoidal” valley response arising from competition among intermediate-state-mediated relaxation channels. These results provide a route to strain-controlled manipulation of long-lived momentum-indirect valley excitons, opening a pathway toward strain-programmable valley engineering in two-dimensional excitonic systems.

The Haldane model represents the minimal lattice-based realization of a Chern insulator, exhibiting a quantized Hall conductance in the absence of Landau levels. Despite its conceptual elegance, the implementation in crystalline solids of the requisite pattern of Peierls phases breaking time-reversal symmetry remains experimentally demanding. In this work, we theoretically investigate the possibility to simulate the Haldane model in ultraclean GaAs/AlGaAs heterostructures. Our proposal relies on recent experiments in which a high-mobility two-dimensional electron gas is subject to a gate-defined honeycomb electrostatic potential and a laterally periodic magnetic field generated by patterned ferromagnetic structures. The combined electrostatic and magnetic superlattices furnish a viable route to emulate the topological properties of the Haldane model.

In realistic nanoscale transport setups, electron-phonon coupling leads to the exchange of heat between phonon baths and electronic reservoirs with finite heat capacities. Such exchange affects the finite reservoir's temperature. However, this sensitivity of the finite reservoir temperature to the exchange of heat with the finite reservoir has remained unexplored for thermometry. Here, we fill this gap by combining current metrology techniques with a thermodynamic framework encompassing finite reservoirs. We focus on an experimentally realizable setup with a quantum dot coupled to a finite reservoir and consider two distinct current-based strategies in the long-time limit, namely monitoring quanta exchanged between the quantum dot and finite reservoir and the measurement of the total current flowing from the quantum dot into an infinite reservoir. A third strategy involves measurements of the quantum dot occupation. For a large but finite reservoir, we show that the Fisher information for all three strategies captures the finite reservoir's contribution to sensitivity through common factors. We also demonstrate that monitoring quanta exchanged between the system and finite reservoir in the long-time limit achieves optimal precision. Finally, we provide an optimization analysis that explores how maximal precision can be achieved within each of the current-based strategies by tuning the gate voltage.