Early investigations on vanadium in the cubic 3C-SiC polytype concluded that the luminescence of the center is not possible because the excited state is degenerate with the conduction band. However, later work refuted this notion, demonstrating a doublet in photoluminescence (PL) at $\sim 1493–1495\mathrm{nm}$, apparently associated with vanadium (V). In this work, we undertake a detailed experimental and theoretical study of the V center in 3C-SiC. We show that the vanadium PL can be seen as a recombination of an exciton bound to V, in contrast to the other two common hexagonal polytypes (4H- and 6H-SiC), where the PL is due to an interatomic transition of the $3d$ electron within the V center, according to a well-established model. We also show that the splitting observed in the PL lines is likely not inherent to the center and is due to stress present in the samples. Ideally, in a strain-free 3C-SiC material, the vanadium PL will comprise a single line, which makes the V center in this polytype attractive for applications as a qubit at moderate temperatures. This contrasts with the hexagonal polytypes where the splitting of the zero-phonon line is inherent to the center due to the crystal structure, which has a negative effect on the spin coherence at liquid helium temperature, and millikelvin temperatures are needed to improve the spin coherence.

We examine nonlinear transport in a viscous two-dimensional electron fluid within narrow GaAs channels. The differential magnetoresistance shows nonmonotonic behavior, a signature of electron pairing in the hydrodynamic regime. Theoretical models that account for both the influence of these interactions on shear stress relaxation and viscosity changes from electron heating show good agreement with the data. The nonlinear regime thus reveals how such correlated states govern the hydrodynamic behavior of the electron fluid. Our findings establish the nonlinear transport regime as a powerful probe for dissecting the complex interplay of correlated electron states and momentum relaxation in the hydrodynamic flow of an electron fluid.

In this work, the band structure of quasi-one-dimensional ${\mathrm{HfSe}}_3$ was investigated with nanospot angle-resolved photoemission spectroscopy (nano-ARPES) in both the $p$- and $s$-polarization geometries and with density functional theory calculations. ${\mathrm{HfSe}}_3$ has a rectangular surface Brillouin zone where the effective hole mass along the chain direction ($\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{Y}}$) measured with $p$-polarization geometry is $-0.27\pm 0.01{\mathrm{m}}_{\mathrm{e}}$, which is smaller than the effective hole mass along the direction perpendicular to the chains measured with $s$-polarization geometry ($\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{B}}$), $-1.17\pm 0.01{\mathrm{m}}_{\mathrm{e}}$, in agreement with the calculated hole masses of $-0.25{\mathrm{m}}_{\mathrm{e}}$ ($\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{Y}}$) and $-1.11{\mathrm{m}}_{\mathrm{e}}$ ($\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{B}}$), respectively. A band separation of $0.22\pm 0.01$ eV is observed at the top of the valence band in the experimental band structure along $\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{Y}}$. This band separation may be partly enhanced due to intrinsic spin-orbit coupling effects, as the band structure calculated with density functional theory shows a significant separation of 0.29 eV, for the two bands closest to the top of the valence band along $\overline{\mathrm{\Gamma }}$ to $\overline{\mathrm{Y}}$, only when spin-orbit interactions are included.

The conditions for the existence of collapsed states of an electron bound to an impurity on the surface of few-layer black phosphorus (BP) are theoretically determined by a model that combines tight-binding and continuum approximations. Under applied vertical bias, the quasiparticle gap of this material significantly decreases and eventually closes at sufficiently high bias. As the bias reduces the gap, the binding energy of an electron bound to a positively charged impurity may reach the energy range where it crosses the valence band, thus characterizing the collapsed impurity state. On the other hand, depending on its orientation, the applied bias may also pull the electron away from the impurity, thus reducing its binding energy and, consequently, preventing the collapse. We demonstrate that the competition between these two phenomena leads to a reentrant behavior of the impurity collapsed state as the applied bias increases. Also, in the case where the BP gap is closed by the bias, low-energy electrons in this material behave as massless Dirac fermions with highly anisotropic Fermi velocity, for which we use a semianalytical method to predict the conditions of applied bias and impurity charge that lead to the impurity collapsed state. The phase diagrams produced in our study will help guide future work towards the observation of such collapsed electron-impurity states in BP.

Contrary to the conventional view that defects degrade electrical transport, we demonstrate through quantum transport calculations that engineering extended line defects in two-dimensional black arsenic (b-$\mathit{As}$) can anomalously enhance electron mobility, electrical conductance, thermoelectric power factor, and figure of merit (ZT). These defects simultaneously suppress lattice thermal conductivity while preserving excellent electrical transport, leading to an over threefold increase in ZT (up to 1.52) compared to pristine b-$\mathit{As}$. This enhancement originates from a resonant coupling between defect-induced bands and intrinsic valence bands—a mechanism absent in black phosphorus due to its out-of-plane $p_z$ orbital character. Our work establishes a general design principle for low-dimensional thermoelectrics: materials with in-plane orbital-dominated band edges are ideal platforms for line-defect engineering toward synergistic optimization of electrical and thermal transport properties.

Two-dimensional (2D) robust intrinsic ferromagnetic (FM) half-metals and semiconductors exhibit widespread application prospects in spintronic and magnetic storage devices. However, designing 2D materials with high Curie temperature still faces significant challenges, as 2D crystals cannot spontaneously form long-range magnetic order at finite temperatures according to the Mermin-Wagner theorem. In this work, combining first-principles and Monte Carlo simulations, we propose a series of 2D intrinsic FM ${\mathrm{Cr}}_2{MX}_4$ ($M=\mathrm{In}$, Ge; $X=\mathrm{S}$, Te) materials with large magnetic moment ($\sim 7{\mu }_B$), high Curie temperatures ($120\sim 638$ K), sizable half-metallic and semiconducting gaps ($1.19\sim 2.94$ eV), and excellent structural stability. The superexchange mechanism mediated by Cr-$X$-Cr interaction is responsible for the FM coupling. High spin states of Cr-$d$ orbitals in the $D_{4h}$ crystal field lead to the large magnetization, the exchange splitting between the $d_{x^2-y^2}$ and $d_{xy}$ orbitals briefly induces a wide gap. Furthermore, the ${\mathrm{Cr}}_2{MX}_4$ shows out-of-plane magnetization with magnetic anisotropy energy (MAE) of $56.76\sim 434.25$ µeV/f.u., and the spin-orbit coupling plays a leading contribution compared to the magnetic dipole-dipole interaction. The origin of MAE is also unveiled by the torque method, second-order perturbation theory, and magnetic dipole-dipole interaction. Under biaxial strain of $-4\%\sim 4\%$, it is tunable for the magnetic exchange, Curie temperature, and magnetic anisotropy energy of ${\mathrm{Cr}}_2{MX}_4$, and the magnetization direction, half-metallic, or semiconducting behaviors are robustly preserved. Our results indicate that ${\mathrm{Cr}}_2{MX}_4$ is likely as candidates of spintronic and magnetic storage devices.

The elemental composition and electronic structure of materials analyzed by electron energy loss spectroscopy (EELS) are probed by the inner-shell ionization of atoms. This is a localized process that can be approximated by the scattering of an electron beam from a free atom. We calculate the inelastic differential cross section perturbatively within the framework of quantum electrodynamics (QED). The interaction between the incoming electron and the atom factorizes into a high-energy electron term and the atomic transition current. The matrix elements of the transition current are computed within the relaxed Dirac-Hartree-Fock method. We analyze the correlation effects arising from the relaxation of the atomic orbitals induced by the creation of a core hole. These effects are particularly relevant in quantum many-body systems and have a significant impact on the shape of the differential cross section near the ionization threshold in EELS spectra. In addition to the continuum, we calculate the discrete excitation spectrum of ${\mathrm{DyScO}}_3$ using crystal-field multiplet theory. The calculated spectrum shows very good agreement with experimental EELS data.

We compute the average density of a three-dimensional multiband crystal of arbitrary symmetry, metal or insulator, to first and second order in a weak homogeneous magnetic field. To linear order and for insulators, the density follows the well-known Streda formula, but for metals there is an extra contribution from the orbital magnetic moments at the Fermi surface. To second order the average density depends on several microscopic processes. Among these, the quantum metric tensor plays an important role by generating a pseudomagnetic moment resulting from the rotation of the Bloch wave functions in the complex projective plane. We also discuss the implications of our results for the volume and pressure. The method we develop is explicitly gauge invariant, considers intraband and interband processes on equal footing, accommodates relaxation processes, and can be readily extended to other observables.

We identify inter-valley scattering as the microscopic origin of anomalous charge transport in n-type $\mathrm{M}{\mathrm{g}}_3{\left(\mathrm{Sb},\mathrm{Bi}\right)}_2$ thermoelectrics. This mechanism depends critically on carrier concentration, as energy conservation governs phonon-assisted inter-valley transitions. We show that reducing the carrier density can eliminate the transport anomaly. A key prediction of this framework, namely the existence of a conductivity minimum below room temperature, had not been observed previously, while this study reveals clear minima at 190 K in ${\mathrm{Mg}}_{3.1}{\mathrm{Sb}}_{1.99}{\mathrm{Te}}_{0.01}$ and 150 K in ${\mathrm{Mg}}_{3.1}{\mathrm{Sb}}_{1.49}{\mathrm{Bi}}_{0.5}{\mathrm{Te}}_{0.01}$. The observed temperatures of these minima are in good agreement with the phonon spectra. Together, these results provide a complete and self-consistent explanation of the long-standing transport anomaly in $\mathrm{M}{\mathrm{g}}_3{\left(\mathrm{Sb},\mathrm{Bi}\right)}_2$.

Scalable spin qubit devices will likely require long-range qubit interconnects. We propose to create such an interconnect with a resistive topgate. The topgate is positively biased to form a channel between the two dots; an end-to-end voltage difference across the nanowire results in an electric field that propels the electron from source dot to target dot. The electron is momentum incoherent but not necessarily spin incoherent; we evaluate threats to spin coherence due to spin-orbit coupling, valley physics, and nuclear spin impurities. We find that spin-orbit coupling is the dominant threat, but momentum-space motional narrowing due to frequent scattering partially protects the electron, resulting in characteristic decoherence lengths $\sim 15$ mm for plausible parameters.

Monolayer lateral heterostructures, an interesting class of nanostructures, have garnered significant attention in optoelectronics and nanoelectronics due to their unique physical properties, yet their radiative heat transfer characteristics remain poorly understood. Here, we take $\mathrm{graphene}\text{−}h\mathrm{BN}$ lateral heterostructures as an example to unveil the emergence of ultrastrong thermophotonic excitations in monolayer lateral architectures, yielding radiative heat transfer that approaches an order of magnitude enhancement over their conventional vertical counterparts. Through a systematic analysis of dispersion evolution and surface wave dynamics, we attribute this enhancement to a pronounced heterointerface effect between surface polaritons supported by the constituent materials. Remarkably, this enhancement mechanism proves robust across diverse material combinations, and its radiative performance is superior to that of numerous classic heterostructures and advanced metasurfaces. These findings position monolayer lateral heterostructures as a promising framework for the manipulation of thermal photonics at the nanoscale, offering fertile ground for future investigations into the roles of exciton dynamics, carrier dynamics, and interfacial quantum effects in electromagnetic energy transport.

The system of Vlasov equations for electrons with a linear Dirac spectrum is solved, and a dispersion equation is derived that describes the influence of a uniform high-frequency electric field on the spectrum and damping rate of two-dimensional terahertz (THz) plasmons in single-layer doped graphene. Our analysis demonstrates that a THz electric field of several tens of kV/cm, applied parallel to the graphene plane, can induce parametric instability of the long-wavelength two-dimensional plasmons. This parametric instability arises from the resonant coupling of plasmon modes, which occurs in a high-frequency electric field due to third-order electrodynamic nonlinearity.

Real band topology often appears in systems with space-time inversion symmetry and is characterized by invariants such as the Euler and second Stiefel-Whitney classes. Here, we examine the generic band topology of Bogoliubov–de Gennes (BdG) Hamiltonians with $C_{2z}T$ symmetry, where $C_{2z}$ and $T$ are twofold rotation about the $z$ axis and time-reversal symmetries, respectively. We discuss the Euler band topology of superfluids and superconductors in the DIII and CI Altland-Zirnbauer symmetry classes, where the Euler class serves as an integer-valued topological invariant of the $4\times 4$ BdG Hamiltonian. Using expressions for the Euler class under $n$-fold rotational symmetry, we derive formulas relating the Euler class to previously known topological invariants of class DIII and CI systems. We demonstrate that three-dimensional class DIII topological phases with an odd winding number, including the B phase of superfluid helium-3, are topological superconductors or superfluids with a nontrivial Euler class. We refer to these as Euler superconductors or superfluids. Specifically, the ${}^3\mathrm{He}\text{−}\mathrm{B}$ superfluid in a magnetic field is identified as an Euler superfluid. Three-dimensional class CI topological phases with twice an odd winding number are also Euler superconductors or superfluids. When spatial inversion symmetry is present, class CI superconductors with a nontrivial Euler class exhibit superconducting nodal lines with a linking structure. This phenomenon is demonstrated using a model of a three-dimensional $s_{\pm }$-wave superconductor. These findings provide a unified framework for exploring Euler band topology in superfluids and superconductors, connecting various phenomena associated with $T$-breaking perturbations, including Majorana Ising susceptibility and higher-order topology.

This Letter presents the theory of planar ballistic superconductor–normal metal–superconductor junctions at $T=0$ for any normal layer thickness $L$ taking into account phase gradients in superconducting leads. The current-phase relation was derived in the model of the steplike pairing potential analytically and is exact in the limit of large ratio of the Fermi energy to the superconducting gap. At small $L$ (short junction) the obtained current-phase relation is essentially different from that in the previous theory neglecting phase gradients. It was confirmed by recent numerical calculations and was observed in the experiment on short InAs nanowire Josephson junctions. The analysis resolves the problem with the charge conservation law in the steplike pairing potential model.

In two-dimensional systems with space-time inversion symmetry, Dirac nodes (DNs) carry non-Abelian topological charges, which induce an intriguing momentum space braiding phenomenon. Although the original idea was proposed in condensed matter setup, the experimental verification of non-Abelian charge conversion has been limited to artificial metamaterials because of the difficulty in identifying suitable materials in which controlled tuning of DN positions is possible. In this work, we propose bilayer binary honeycomb lattices (BBHLs) as a material platform to study the non-Abelian charge conversion phenomenon in which DN positions in momentum space can be manipulated. More explicitly, we demonstrate that layer sliding and vertical pressure serve as tunable braiding parameters controlling the non-Abelian charge conversion process, which is crucial to understand the stacking-dependent electronic properties of BBHL systems. We show that the BBHL systems are a promising candidate for the experimental realization of non-Abelian phenomena of DNs in condensed matter.

We present a large-scale simulation of the three-dimensional and mean-field spin glasses down to a very low but finite temperature. We extrapolate pertinent observables, e.g., the disorder-averaged central weight to zero temperature, finding that many thermodynamic states at a finite temperature and two ground states at zero temperature are fully compatible. While the disorder-averaged central weight monotonically decreases with decreasing temperature, this is far from true for individual samples. This motivates us to link this behavior with the well-known temperature chaos. At an observing temperature, a sample may or may not have pure state coexistence depending on whether it is undergoing temperature chaos, which is a random process. Therefore, temperature chaos is likely responsible for the emergence of many pure states, providing a natural and intuitive explanation for the coexistence of expensive domain-wall excitations and many pure states at the disorder-averaged level.

We investigate spin-charge conversion in exchange-biased NiFe/IrMn heterostructures, where spin-polarized electrons are generated in the NiFe layer by ferromagnetic resonance and transferred by diffusion into adjacent layers. The conversion of spin current into charge current via the inverse spin Hall effect is governed by the competition between skew scattering and side-jump scattering, which produces a minimum in the temperature dependence of the conductivity. By introducing different nonmagnetic spacers, we identified the localization of the dominant scattering processes. In NiFe, NiFe/IrMn, and NiFe/Cu/IrMn structures, the conductivity minimum occurs at $T\approx 95$ K, reflecting scattering in the NiFe layer, with the amplitude gradually reduced by increasing Cu thickness. In contrast, insertion of a Ta spacer shifts the minimum to $T\approx 265$ K due to strong spin-orbit coupling and a short spin diffusion length that transfer the scattering into the Ta layer. These results demonstrate how the choice of spacer material enables control of spin scattering and spin-charge conversion, providing guidelines for the design of exchange-biased heterostructures for spintronic applications.