Spin textures in spintronic materials, driven by spin-orbit interaction, are inherently complex, making their description with a simple Hamiltonian particularly challenging. Although k·p models have been employed to approximate these textures, further simplification is needed to capture the full complexity of the system. This study investigates the spintronic properties of two polar oxide perovskites, ${\mathrm{BiInO}}_3$ and ${\mathrm{TlIO}}_3$, using density functional theory. Both materials are wide band-gap semiconductors and exhibit unique anomalous spin textures. A pair of analytical models, ${\mathcal{H}}_{MJ1}$ and ${\mathcal{H}}_{\mathrm{MJ}2},$ are introduced that precisely mirror the observed spin textures in these materials. The Hamiltonian ${\mathcal{H}}_{\mathrm{MJ}1}$ reshapes the existing paradigm, providing a more robust and versatile framework than earlier-proposed Hamiltonian ${\mathcal{H}}_{\mathrm{RD}}$. It encapsulates two distinct spin textures: a unidirectional, momentum-independent persistent spin texture (PST), and a bidirectional (partial) PST, both essential for advancing the study of nonballistic spin field-effect transistors. In contrast, Hamiltonian ${\mathcal{H}}_{\mathrm{MJ}2}$ reproduces spiral spin texture. Extending the Rashba, Dresselhaus, and Weyl models, this study introduces refined analytical models that effectively capture the complexity of spin textures emerging from sophisticated spin-orbit interactions.

Nonreciprocal devices are key components in modern electronics covering broad applications ranging from transistors to logic circuits owing to the output rectified signal in the direction parallel to the input. In this Letter, we propose a transverse Cooper-pair rectifier in which a nonreciprocal current is perpendicular to the driving field, when inversion, time-reversal, and mirror symmetries are broken simultaneously. The Blonder-Tinkham-Klapwijk formalism is developed to describe the transverse current-voltage relation in a normal-metal–superconductor tunneling junction, where symmetry constraints are achieved by an effective built-in supercurrent manifesting in an asymmetric and anisotropic Andreev reflection. The asymmetry in the Andreev reflection is induced when inversion and time-reversal symmetry are broken by the supercurrent component parallel to the junction while the anisotropy occurs when the mirror symmetry with respect to the normal of the junction interface is broken by the perpendicular supercurrent component to the junction. Compared to the conventional longitudinal one, the transverse rectifier supports fully polarized diode efficiency and colossal nonreciprocal conductance rectification, completely decoupling the path of the input excitation from the output rectified signal. This Letter provides a formalism for realizing transverse nonreciprocity in superconducting junctions, which is expected to be achieved by modifying current experimental setups and may pave the way for future low-dissipation superconducting electronics.

As divacancy (VV) and nitrogen-vacancy (NV) color centers in $4H$-SiC have attracted significant interest for their potential in quantum technologies, the origins of the photoluminescence (PL) signals (such as PL5–PL8) observed near the VVs signals (PL1–PL4) remain a mystery. In this paper, multiple defect clusters are designed by combining VVs with intrinsic defects and the common extrinsic elements including oxygen, nitrogen, and hydrogen. Based on the first-principles calculations of the spin configuration, formation energy, zero-phonon line, and zero-field splitting, two configurations of $\mathrm{O}{\mathrm{V}}^0$ (one oxygen atom filling the carbon vacancy in $\mathrm{V}{\mathrm{V}}^0$) are attributed for PL5 and PL6, and one configuration of $\mathrm{NH}{\mathrm{V}}^0$ (one hydrogen atom attached to the nitrogen atom in $\mathrm{N}{\mathrm{V}}^0$) is the source of PL8. Further radiative lifetime calculations confirm that these defect clusters are good single-photon sources. Additionally, we found that the $\mathrm{OH}{\mathrm{V}}^{+}$ (OV with one hydrogen atom bonded with the oxygen atom at +1 charge state) are potential color centers with $S$ = 1. In this paper, we provide theoretical insights not only into the preparation of color centers such as PL5, PL6, and PL8 but also into developing color centers that are related to VVs.

The Kekulé-Kitaev model, an extension of the Kitaev model, exhibits quantum spin liquid properties, which has an exact solution through Kitaev parton construction. In this study, we calculate the dynamical spin structure factor as a linear response and the third-order magnetic susceptibility as a nonlinear response using two-dimensional coherent spectroscopy for the Kekulé-Kitaev model. Our results reveal that the few-matter fermion excitations approximation provides reliable results for both linear and nonlinear responses. Notably, while the Kekulé-Kitaev model shows linear and nonlinear responses qualitatively similar to the Kitaev model, it displays distinct behavior under a weak uniform and staggered magnetic field. Specifically, the Kekulé-Kitaev model does not present a non-Abelian phase under a uniform magnetic field, while such phase appears in the presence of a staggered magnetic field. Interestingly, within the non-Abelian phase, signals originating from two nonadjacent fluxes in the nonlinear response are stronger than signals from other flux excitations. Furthermore, we demonstrate that the ground state of the Kekulé-Kitaev model at isotropic coupling is mapped, through unitary spin rotations, to an excited state of the Kitaev model with a uniform flux configuration.

Exchange bias (EB) related to magnetization reversal fields was found in a single-crystal of ${\mathrm{Ni}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$, a compensated ferrimagnet consisting of two $\mathrm{N}{\mathrm{i}}^{2+}$ ferromagnetic sublattices with opposite moments, associated with two differently distorted honeycomb-like layers in the ab plane, alternating along the $c$ axis. The EB field is significant near the compensation temperature $T_{\mathrm{comp}}=33\mathrm{K}$, it increases rapidly as the temperature approaches $T_{\mathrm{comp}}$, and changes sign when crossing $T_{\mathrm{comp}}$, showing a large gap of 3.5 kOe. The magnetization reversal field also diverges at $T_{\mathrm{comp}}$ and reaches 10 kOe. The hyperbola-like spin reversal lines obtained in the $T\text{−}H$ plane are asymmetric with respect to the $H=0$ and $T=T_{\mathrm{comp}}$ axes due to EB and demonstrate both the field and temperature EB effect. These lines exhibit mirror symmetry when the sign of $H_{\mathrm{cool}}$ changes, which makes it possible to determine the EB energy to be about 100 erg/g. Noninterface EB in single-phase ${\mathrm{Ni}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$ is discussed within the model of two antiferromagnetically coupled $\mathrm{N}{\mathrm{i}}^{2+}$ sublattices with oppositely oriented ferromagnetic moments and is compared with a similar EB observed in another type of compensated ferrimagnet – orthoferrite ${\mathrm{ErFeO}}_3$.

We present analysis of temperature- and field-dependent magnetic order and Néel transition in monolayered ${\mathrm{FePS}}_3$, exhibiting a zigzag antiferromagnetic (zAFM) order below a Néel temperature ($T_{\mathrm{N}}$) of 120 K, using a combination of first-principles density functional theoretical calculations, effective spin Hamiltonian, and Monte Carlo simulations. As a consequence of spin-phonon coupling, the honeycomb lattice of Fe ions distorts upon zAFM ordering, with ferromagnetic chains exhibiting long intrachain Fe-Fe bonds and short interchain Fe-Fe bonds. We construct an effective spin Hamiltonian to capture low-energy physics determining exchange interactions from first-principles using the four-state method. Analyzing this spin Hamiltonian with Monte Carlo (MC) simulations, we estimate $T_{\mathrm{N}}$ (85 K), which changes upon quantum correction to 127 K, closer to the experimental $T_{\mathrm{N}}$ of 120 K. Our low temperature- and field-dependent MC simulations capture the experimentally observed plateau in $M$ versus $H$ at the half-magnetization and reveal its magnetic structure: the half-plateau phase (HPP) exhibits a structure cell-doubled along the chain direction ($a$ axis) of zAFM state, with ferromagnetic ($\uparrow \uparrow \uparrow \uparrow$) and antiferromagnetic ($\uparrow \uparrow \downarrow \downarrow$) chains alternating along $b$ axis. Density functional theoretical calculations reveal that the HPP exhibits a gap of 0.6 (1.27) eV in electronic bands of down (up)-spin channel. Our MC simulations reveal domains with distinct orientations of HPP at higher fields and transformation to ferromagnetic (FM) state at $H>60$ T, which is overestimated relative to the experiments at $H_c\sim 40$ T. The FM state of monolayered ${\mathrm{FePS}}_3$ is half-metallic with a gap of 2.2 eV in the majority-spin channel. We find that the coupling of phonons with orbital moments is weak, while that with spins is moderate, and predict phonon anomalies at $T_{\mathrm{N}}$.

We present a generalization of the discrete Lehmann representation (DLR) to three-point correlation and vertex functions in imaginary time and Matsubara frequency. The representation takes the form of a linear combination of judiciously chosen exponentials in imaginary time, and products of simple poles in Matsubara frequency, which are universal for a given temperature and energy cutoff. We present a systematic algorithm to generate compact sampling grids, from which the coefficients of such an expansion can be obtained by solving a linear system. We show that the explicit form of the representation can be used to evaluate diagrammatic expressions involving infinite Matsubara sums, such as polarization functions or self-energies, with controllable, high-order accuracy. This collection of techniques establishes a framework through which methods involving three-point objects can be implemented robustly, with a substantially reduced computational cost and memory footprint.

Tunneling spectroscopy is an important tool for the study of both real- and momentum-space electronic structure of correlated electron systems. However, such measurements often yield noisy data. Machine learning provides techniques to reduce the noise in postprocessing, but traditionally requires noiseless examples which are unavailable for scientific experiments. In this work we adapt the unsupervised Noise2Noise and self-supervised Noise2Self algorithms, which allow for denoising without clean examples, to denoise quasiparticle interference data. We first apply the techniques on simulated data, and demonstrate that we are able to reduce the noise while preserving finer details, all while outperforming more traditional denoising techniques. We then apply the Noise2Self technique to experimental data from an overdoped cuprate [(Pb,${\mathrm{Bi})}_2{\mathrm{Sr}}_2{\mathrm{CuO}}_{6+\delta }]$ sample. Denoising enhances the clarity of quasiparticle interference patterns, and helps to obtain a precise extraction of electronic structure parameters. Self-supervised denoising is a promising tool for denoising quasiparticle interference data, facilitating deeper insights into the physics of complex materials.

We have investigated the structural and electronic properties of 3 at. % Yb-doped ${\mathrm{SrTiO}}_3$/Si(001) grown by molecular beam epitaxy. Other rare-earth dopants that result in $n$-type conductivity typically substitute for Sr at the $A$ sites in the $AB{\mathrm{O}}_3$ perovskite lattice. In contrast, Yb is shown to substitute predominantly for Ti at the perovskite $B$ sites based on data from atomically resolved scanning transmission electron microscopy and energy dispersive spectroscopy, as well as extended x-ray absorption fine structure measurements. An atom beam flux (Θ) mismatch was present during film growth because it was assumed that Yb would occupy $A$ sites. As a result of this assumption, the fluxes were set such that ${\mathrm{\Theta }}_{\mathrm{Yb}}+{\mathrm{\Theta }}_{\mathrm{Sr}}={\mathrm{\Theta }}_{\mathrm{Ti}}$. The formation of ${\mathrm{Yb}}_{\mathrm{Ti}}$ rather than ${\mathrm{Yb}}_{\mathrm{Sr}}$ results in Sr vacancies and extraneous (i.e., nonlattice) Ti atoms in the films. Yb exhibits two distinct charge states as determined by x-ray absorption spectroscopy and associated theoretical modeling, $+2.7$ and $+2.1$. These aliovalent dopants are compensated by donor electrons from oxygen vacancies that form during film growth. The defect complexes resulting from the flux mismatch, together with oxygen vacancies, lead to deep-level electron traps that were detected by resonant photoemission and predicted to be stable by ab initio theory, as well as much higher sheet resistance than that associated with, for instance, La-doped ${\mathrm{SrTiO}}_3$ (STO) films. Ab initio calculations show that the preference for $B$-site occupancy is driven by low oxygen chemical potential at the growth front as required to deposit STO on Si without ${\mathrm{SiO}}_2$ formation.

Single coherent photons on demand are essential inputs for many applications of quantum optics, including for linear optical quantum computing. One critical parameter when assessing the potential of a material to emit coherent single photons is the homogeneous linewidth, the measurement of which is often obscured by fast spectral fluctuations. Photon correlation Fourier spectroscopy (PCFS) provides a more accurate measurement of the homogeneous emission linewidth than traditional techniques by probing the system on timescales faster than spectral diffusion. However, PCFS is limited by the long integration times it requires, restricting its use to only the most stable materials and making it difficult to study large numbers of emitters within these select samples. Our group previously developed a machine-learning (ML) algorithm to denoise PCFS signals which showed promise on a single experimental dataset but was difficult to further validate. Here, we demonstrate the use of a similar ML model to accelerate PCFS experiments by an order of magnitude and verify its accuracy on a statistical number of samples. We use 10% of the photon stream from full PCFS experiments to replicate shorter measurements, resulting in data with prohibitively high levels of noise. By employing a denoising autoencoder neural network, we extract the underlying signal from the noisy truncated measurements and unambiguously verify the results of the reconstructions through direct comparison with the original experiments. We confirm the generalization of the ML treatment through application to >80 experiments from multiple samples including $\mathrm{CsPbB}{\mathrm{r}}_3$ and InP/ZnSe/ZnS nanocrystals. The large-scale verification of the ML reconstructions enables confident use of ML to accelerate future PCFS experiments up to 10×, enhancing the practical capabilities of this technique and further promoting the application of ML to other spectroscopic methods.

We develop a theory of Coulomb blockade oscillations in transport and thermodynamic properties of a mesoscopic device having multiple charging energy modes. This setup can be realized using a nanoelectronic circuit comprising coupled hybrid metal-semiconductor islands. We show that this device can have various distinctive operational regimes depending on the strength of charging modes and base temperature. We focus on three different regimes: quantum regime, thermal regime and quantum-thermal mixed regime, in which the shape of the Coulomb blockade oscillations manifests well-defined features that can be accessed via conductance measurements. Our theory covers full crossover among these regimes and also accounts for an accidental vanishing of one of the charging modes.

The two-dimensional (2D) homogeneous electron gas (HEG) is a fundamental model in quantum many-body physics. It is important to theoretical and computational studies, where exchange-correlation energies computed in it serve as the foundation for density-functional calculations. It is also of direct relevance to a variety of experimental settings, especially with the rapid recent growth in 2D materials and moiré systems. In these experiments, metallic gates are often present, which screen the Coulomb interaction between electrons. The effect of the screening can qualitatively change the behavior of the 2D HEG, and requires accurate many-body computations to capture. In this paper, we perform state-of-the-art diffusion Monte Carlo (DMC) calculations in the 2D HEG subjected to symmetric dual-gate screening. We systematically compute the correlation energy across a range of densities and gate separations for both spin unpolarized and fully polarized systems. A global fit is obtained for the correlation energy, using these data and imposing various limiting behaviors obtained from perturbation analysis. The functional will allow density-functional calculations to be performed for a variety of realistic experimental setups, which can accurately account for the presence of gates. We also investigate how the gate screening affects the bulk modulus, pair correlation function, and the structure factor of the 2D HEG, which can potentially be probed in experiments.

The Be-related ultraviolet luminescence band with a maximum at about $3.38\mathrm{eV}$ in GaN:Be is caused by the shallowest acceptor in GaN with the −/0 transition level at $0.113\mathrm{eV}$ above the valence band. The luminescent properties of this acceptor were studied in detail. First-principles calculations identify this acceptor as the ${\mathrm{Be}}_{\mathrm{Ga}}{\mathrm{O}}_{\mathrm{N}}{\mathrm{Be}}_{\mathrm{Ga}}$ complex. These calculations also predict a deep level, at $0.34\mathrm{eV}$ above the valence band. However, we were not able to find evidence for this level in photoluminescence experiments.

We demonstrate that nanoconfinement effects and in-plane magnetic anisotropy (IMA) can lead to tilted chiral spin textures in magnetic nanostructures, based on the analysis and simulation of theoretical models of micromagnetism. The tilted skyrmions are induced in confined nanoscale magnets with IMA under perpendicular magnetic fields. The chiral magnetic structures depend significantly on the size of the nanostructures. A controlled string of periodic skyrmion states emerges within the central magnetic domain wall, which can be tuned by the steady magnetic fields and the size of the nanostructures. Nontrivial topological states with noninteger topological charges are achieved by tuning the magnetic fields or the sizes of the nanostructures. Importantly, the periodic switching between the trivial and the nontrivial topological configurations is realized using an alternating magnetic field. Our study reveals an important mechanism for controlling novel skyrmion states via nanoconfinement effects and the IMA in magnetic nanostructures, and also provides a new approach for the development of magnetic field-modulated spin nanodevices.

Extension of coherence time is a desired goal in the field of all-optical information processing implemented in both classical and quantum ways. Here we show how the decay time of a coherent signal from localized excitons can be significantly increased utilizing the spin degree of freedom. To experimentally demonstrate this effect, we studied three-pulse photon echoes from excitons in a single InGaAs/GaAs quantum well subject to a transverse magnetic field. Field-induced quantum beats lead to oscillation of the exciton population between short-lived bright and long-lived dark states during the coherence storage period between the second and third excitation pulses. In the aperiodic regime, the echo signal decay time tends to the dark exciton lifetime, which leads to an increase in the photon echo decay time by an order of magnitude.

Complex-frequency calculation enables the characterization of open wave systems in the complex frequency plane as well as the evaluation of wave behaviors under virtual gain and/or loss, which has widespread applications in the investigations of wave scattering and non-Hermitian physics. The corresponding calculation approaches, however, have not been well developed and are usually limited to simple analytical models. Here, we report an efficient numerical method for calculating complex-frequency acoustic wave fields, in which the imaginary part of the frequency is equivalently converted into the variation in material parameters. In this way, the complex-frequency problem becomes a real-frequency one which can then be readily implemented with most existing numerical solvers of the Helmholtz equation. The proposed method is validated by considering two representative examples: the scattering of a one-port lossy acoustic resonator and the imaging of a lossy acoustic superlens under complex frequency excitation. Our work provides a practical and general solution for complex-frequency calculation, in principle, applicable to any complex, dispersive wave systems, which could serve as a powerful tool for fundamental and applied research related to wave scattering and non-Hermiticity.