Fluctuations in disordered matter play a central role in determining material properties and physical responses. Recent studies have identified an exotic class of systems known as structurally hyperuniform materials, in which large-scale density fluctuations are anomalously suppressed through special spatial organization of particles, phases, or microstructural features. Here we demonstrate that ordinary, structurally nonhyperuniform disordered materials can nevertheless support hyperuniform physical source fields, including scalar, vector, or tensor observables such as incompatibility, bound charge, and bound current. These sources can also regularize the response fields they drive. We develop a general theoretical framework in which a physical field is generated from a more primitive parent field through a local physical operator. In Fourier space, the spectrum of the derived field is determined by the product of the parent-field spectrum and the Fourier symbol of the operator. When the operator has a small-wave-number zero of order $m$, the derived source spectrum is suppressed by $k^{2m}$ relative to the parent spectrum in the coupled spectral channels. For a parent spectrum scaling as $k^{\alpha }$, hyperuniformity is guaranteed if $\alpha +2m>0$, provided the assumed infrared scaling holds; sufficiently infrared-divergent parent fluctuations need not yield a hyperuniform source. We demonstrate this mechanism in elastic, electrostatic, and magnetostatic settings, showing that operator-generated incompatibility, bound charge, and bound-current fields can become hyperuniform even when their parent eigenstrain, polarization, or magnetization fields remain conventionally disordered. These findings identify a general, explicitly conditional route to field hyperuniformity through local physical constraints and distinguish hyperuniform source generation from regularization of the resulting response fields.

Using first-principles calculations, we investigate how homogeneous strain and crystallographic surface orientation modify the vibrational and superconducting properties of niobium. For bulk Nb, tensile strain strongly softens the phonon spectrum and enhances the electron-phonon coupling, increasing the superconducting transition temperature within the harmonic approximation from 9.5 K at equilibrium to 14.6 K at $\sim 6\%$ lattice expansion. Anharmonic corrections are small near equilibrium but become increasingly significant under tensile strain and considerably reduce this enhancement at large expansion. For ultrathin Nb slabs with low-index (001), (110), and (111) surface orientations, harmonic phonon calculations exhibit imaginary modes, showing that anharmonic lattice effects are essential. To treat these effects efficiently, we train Nb-specific machine-learning interatomic potentials on bulk and slab first-principles configurations and use them to accelerate stochastic self-consistent harmonic approximation calculations, thereby obtaining anharmonically renormalized phonon modes that are combined with density-functional perturbation theory electron–phonon matrix elements to construct the Eliashberg spectral function. Among the three clean free-standing slabs examined, Nb(001) exhibits the strongest electron-phonon coupling and the highest calculated transition temperature of 10.1 K, while Nb(110) and Nb(111) show progressively reduced pairing strength. Finally, by analyzing the Eliashberg spectral function and the functional derivative $\delta T_{\text{c}}/\delta {\alpha }^{2}F\left(\omega \right)$, we identify the phonon energy ranges most effective for superconducting pairing. Our results show that strain, surface termination, and anharmonic phonon renormalization provide complementary and interrelated microscopic routes for tuning superconductivity in Nb.

We investigate the emergence of a scarred discrete time crystal (SDTC) phase in a periodically driven dimerized spin chain. While generic interacting Floquet systems are expected to thermalize according to the eigenstate thermalization hypothesis (ETH), we demonstrate that this system hosts quantum many-body scars (QMBS) that induce a regime of weak ergodicity breaking. Through an analysis of Floquet level statistics, entanglement entropy, and eigenstate fidelity, we identify a manifold of low-entanglement states characterized by semi-Poisson statistics embedded within an otherwise thermal spectrum. These scarred states support robust subharmonic oscillations with period doubling, signaling the spontaneous breaking of discrete time-translation symmetry. We show that the SDTC response is robust against a variety of initial state configurations, demonstrating its stability beyond fine-tuned conditions. A finite-size scaling analysis reveals that the time-crystalline lifetime grows with system size within the range accessible to our exact-diagonalization calculations. However, drawing on the general phenomenology of approximate many-body scars, we expect that hybridization between Floquet scars and the thermal continuum will eventually curtail this growth, causing the lifetime to saturate at system sizes beyond our current numerical reach. This characterizes the SDTC as a long-lived metastable dynamical regime rather than a strictly stable thermodynamic phase, providing a comprehensive framework for understanding the interplay between periodic driving and constrained many-body dynamics in disorder-free systems.

Two-dimensional (2D) multiferroics offer an appealing platform for electrically and magnetically reconfigurable nonlinear photoresponses. In particular, the bulk photovoltaic (BPV) effect, as a second-order nonlinear optical response rooted in Bloch wave quantum geometry, is highly sensitive to crystalline and magnetic symmetries. Therefore, the BPV effect could serve as a sensitive method to capture subtle symmetries in multiferroic systems with fruitful ferroic order switching. Here, taking a monolayer multiferroic $\mathrm{CuCr}{\mathrm{P}}_2{\mathrm{S}}_6$ as a representative example, we systematically investigate the BPV effect across the paraelectric-ferroelectric-antiferroelectric phase transition by combining first-principles calculations with magnetic group symmetry analysis. We explore the influence of phase transition, polarization reversal, multiferroicity, magnetic order, magnetocrystalline anisotropy, and its emergent altermagnetism on the BPV responses. Our results suggest that the BPV effect can effectively distinguish distinct polarization and magnetic states, establishing monolayer $\mathrm{CuCr}{\mathrm{P}}_2{\mathrm{S}}_6$ as a promising 2D multiferroic platform for electrically and magnetically reconfigurable BPV and nonlinear optoelectronic devices.

We report on current-induced spin–orbit torques and field-free magnetization switching in a two-dimensional van der Waals heterostructure consisting of ${\text{WTe}}_2$ as the spin source and ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ as the magnetic layer. Harmonic magneto-optical Kerr effect measurements enable the disentanglement of torque components arising from out-of-plane and in-plane spin accumulations generated by charge transport in ${\text{WTe}}_2$. Our analysis reveals a dominant contribution from out-of-plane spins, yielding a field-like torque efficiency of approximately $8.8\%$, and a damping-like torque efficiency arising from in-plane spins of $1.8\%$ at $150\mathrm{K}$. We observe deterministic bipolar field-free switching of the perpendicular magnetization of ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ up to the Curie temperature, consistent with the strong torque generated by out-of-plane spins. The switching efficiencies extracted from current-induced magnetization reversal and hysteresis loop shifts exceed the intrinsic torque efficiencies measured by harmonic magneto-optical Kerr effect by more than one order of magnitude. The switching efficiencies scale with the temperature-dependent coercivity of the ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ flake, indicating that they reflect a combination of thermal effects assisting magnetization reversal and different torque components. Our results provide a quantitative assessment of unconventional spin–orbit torques in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2/{\text{WTe}}_2$ and emphasize the importance of carefully interpreting torque efficiencies derived from switching-based measurements, particularly in van der Waals systems with Curie temperatures near or below room temperature.

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.

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.

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.

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.

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.