Non-Hermitian topological phases can produce some remarkable properties, compared with their Hermitian counterpart, such as the breakdown of conventional bulk-boundary correspondence and the non-Hermitian topological edge mode. Here, we introduce several algorithms with multilayer perceptron (MLP), and convolutional neural network (CNN) in the field of deep learning, to predict the winding of eigenvalue non-Hermitian Hamiltonians. Subsequently, we use the smallest module of the periodic circuit as one unit to construct high-dimensional circuit data features. Further, we use the Dense Convolutional Network (DenseNet), a type of convolutional neural network that utilizes dense connections between layers to design a non-Hermitian topolectrical Chern circuit, as the DenseNet algorithm is more suitable for processing high-dimensional data. Our results demonstrate the effectiveness of the deep learning network in capturing the global topological characteristics of a non-Hermitian system based on training data.

$\mathrm{SU}\left(N\right)$ symmetry is incompatible with the many-body localized (MBL) phase, even when strong disorder is present. However, recent studies have shown that finite-size $\mathrm{SU}\left(2\right)$ systems exhibit nonergodic, subthermal behavior, characterized by the breakdown of the eigenstate thermalization hypothesis, and by the excited eigenstates entanglement entropy that is intermediate between area and volume law. In this paper, we extend previous studies of the $\mathrm{SU}\left(2\right)$-symmetric disordered Heisenberg model to larger systems, using the time-dependent density matrix renormalization group (tDMRG) method. We simulate quench dynamics from weakly entangled initial states up to long times, finding robust subthermal behavior at stronger disorder. Although we find an increased tendency towards thermalization at larger system sizes, the subthermal regime persists at intermediate time scales, nevertheless, and therefore should be accessible experimentally. At weaker disorder, we observe signatures of thermalization; however, entanglement entropy exhibits slow sublinear growth, in contrast to conventional thermalizing systems. Furthermore, we study dynamics of the $\mathrm{SU}\left(3\right)$-symmetric disordered Heisenberg model. Similarly, strong disorder drives the system into subthermal regime, albeit thermalizing phase is broader compared to the $\mathrm{SU}\left(2\right)$ case. Our findings demonstrate the robustness of the subthermal regime in spin chains with non-Abelian continuous symmetry, and are consistent with eventual thermalization at large system sizes and long time scales, suggested by previous studies.

Bilayer antiferromagnets ${\text{Cr}X}_3$ $(X=\mathrm{Cl}, \mathrm{Br}, \text{and} \mathrm{I})$ are promising materials for spintronics and optoelectronics that are rooted in their peculiar electronic structures. However, their bands are often hybridized from the interlayer antiferromagnetic ordering, thus they are difficult to disentangle by traditional methods. In this work, we show theoretically that nonlinear harmonic spectra can reveal subtle differences in their electronic states. In contrast to prior nonlinear optical studies, which often use one- or two-photon energies, we systematically study the wavelength-dependent nonlinear harmonic spectra realized by hundreds of individual dynamical simulations under changed photon energies. Through turning on and off some excitation channels, we can pinpoint every dipole-allowed transition that largely contributes to the second and third harmonics. With the help of momentum matrix elements, highly entangled resonance peaks at a higher energy above the band edge can be assigned to specific transitions between the valence bands and three separate regions of conduction bands. Our findings demonstrate a feasible means to detect very complex electronic structures in an important family of two-dimensional antiferromagnets.

The dynamic matrix method was employed to perform theoretical calculations for investigating both static and dynamic characteristics of thick ferromagnetic films. This approach considers situations where a noncollinear equilibrium magnetization exists along the thickness due to a thickness-dependent uniaxial anisotropy and interfacial interactions in a synthetic antiferromagnet. In the former scenario, the study exposes a correlation between noncollinear static magnetization and a nonmonotonic dependence of ferromagnetic resonance frequency, where a frequency decrease is observed at low fields in the unsaturated regime. Regarding the synthetic antiferromagnet structure, the research demonstrates noncoherent magnetization rotation in the spin-flop regime, with twisted magnetization states influencing the critical and nucleation fields that define the spin-flop region. The results of the investigation were compared to the macrospin approach, where the magnetization is assumed to be uniform along the thickness. The study suggests that the contribution of noncollinear magnetic moments may mimic the role of the biquadratic interaction in the macrospin model, implying that such a biquadratic term may be overestimated in coupled ferromagnetic films with thicknesses exceeding the material's intrinsic exchange length. Finally, the model was compared with experimental data obtained from a Py/Ir/Py synthetic antiferromagnet, demonstrating that the theoretical consideration of a twisting equilibrium state of the magnetization precisely reproduces the observed dynamic and static properties of the nanostructure.

The effect of impurities on a superconductor with Bogoliubov Fermi surfaces (BFSs) is studied using a realistic tight-binding model. Based on the band structure composed of $d$-orbitals in tetragonal $\mathrm{FeSe}$, whose S-doped sample is a potential material for a BFS, we construct the superconducting state by introducing a time-reversal broken pair potential in terms of the band index. We further consider the effect of impurities on the BFS, where the impurity potential is defined as a local potential for the original $d$-orbitals. The self-energy is calculated using the (self-consistent) Born approximation, which shows an enhancement of the single-particle spectral weight on the Fermi surface. This is consistent with the previous phenomenological theory and is justified by the present more detailed calculation based on the $\mathrm{FeSe}$-based material.

We demonstrate that the photoelectron counting rate, $P^{\left(2\right)}$, measured in two-electron coincidence spectroscopy experiments, provides insight into the nature of topological superconductivity. In particular, we show that the spin dependence of $P^{\left(2\right)}$ allows one to detect superconducting spin-triplet correlations that are induced in a topological superconductor even in the absence of an associated triplet superconducting order parameter. This ability to detect spin-triplet correlations allows one to distinguish between two recently proposed scenarios for the microscopic origin of topological superconductivity in ${\mathrm{FeSe}}_{0.45}{\mathrm{Te}}_{0.55}$. Finally, we show that $P^{\left(2\right)}$ exhibits a characteristic intensity maximum that can be employed to detect topological phase transitions.

Hydrogen $\left({\mathrm{H}}_2\right)$ and helium (He), the most abundant elements in the universe, pose a unique challenge in measuring the equation of state of the mixture, owing to their differing physical properties. There remains a need for data with high enough precision to discriminate between existing equation of state (EOS) mix models in order to understand the internal structure of gas-giant planets. Here, we have measured the EOS of precompressed ${\mathrm{H}}_2\text{−}\mathrm{He}$ mixtures at conditions directly relevant to the planetary interiors using hypervelocity gas guns and Sandia's Z machine with less than 10% uncertainty in density, enabling validation of mixture models. We precompressed 50:50 molar mixtures of ${\mathrm{H}}_2$-He to 0.1–0.2 GPa and directly measured particle velocity (in gas-gun experiments) and shock velocities (in Z-machine experiments). To complement the experimental efforts, we also computed the Hugoniots of precompressed ${\mathrm{H}}_2$-He mixtures using density-functional-theory-based molecular dynamics. We observe approximately 3- to 4.3-fold density compression at pressures up to 44 GPa.

The interplay between a magnetic field and the Coulomb potential from a charged vacancy on the electron states in graphene is investigated within the tight-binding model. The Coulomb potential removes locally Landau level degeneracy, while the vacancy introduces a satellite level next to the normal Landau level. These satellite levels are found throughout the positive-energy region, but in the negative-energy region, they turn into atomic collapse resonances. Crossings between Landau levels with different angular quantum number $m$ are found. Unlike the point impurity system in which an anticrossing occurs between Landau levels of the same $m$, in this work anticrossing is found between the normal Landau level and the vacancy-induced level. The atomic collapse resonance hybridizes with the Landau levels. The charge at which the lowest Landau level $m=-1,N=1$ crosses $E=0$ increases with enhancing magnetic field. A Landau level scaling anomaly occurs when the charge is larger than the critical charge $\beta \approx 0.6$ and this critical charge is independent of the magnetic field.

Positron annihilation lifetime spectroscopy is a unique technique to probe the defect structure of crystalline solids. To distinguish different defect states, accurate calculation of the positron annihilation lifetimes is demanded to compare with the experimental results. We perform quantum Monte Carlo calculations to compute the electron-positron correlation energy and pair correlation function at several electron-positron density ratios. This approach enables us to obtain new fitting parameters under the local density approximation to combine with two-component density functional theory to calculate the positron lifetimes of defect-free bulk and monovacancy defects in various materials. As compared with the experimental results, this method outperformed some previous schemes and provided theoretical support for the previous deduction of certain vacancy defects.

Floquet engineering provides an optical means to manipulate electronic bandstructures, however, carriers excited by the pump field can lead to an effective heating, and can obscure measurement of the band changes. Here, we use multidimensional coherent spectroscopy to create a coherent ensemble of excitons in monolayer ${\mathrm{WS}}_2$ and measure the evolution of the coherence throughout the duration of the Floquet pump pulses with constant fluence but varying pulse duration. Changes to the amplitude of the macroscopic coherence quantifies the additional broadening introduced by interactions with carriers excited via two-photon absorption of the red-detuned pump. At the same time, the evolution of the average phase allows the instantaneous changes to the bandstructure to be quantified, which is demonstrated to be independent of the additional broadening. This approach to measuring the evolution of Floquet-Bloch states demonstrates a means to quantify effective heating and nonadiabaticity caused by excited carriers, while at the same time resolving the coherent evolution of the bandstructure.

We have grown a series of single crystals of two-dimensional van der Waals ferromagnet $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ substituted with Co or Ni. The large single crystals of ${\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{C}{\mathrm{o}}_x\right)}_3\mathrm{GaT}{\mathrm{e}}_2 (0\le x\le 0.55)$ and ${\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{N}{\mathrm{i}}_x\right)}_3\mathrm{GaT}{\mathrm{e}}_2 (0\le x\le 0.46)$ were characterized with x-ray diffraction, magnetic susceptibility, electrical resistivity, and Hall measurements. Our results show that the magnetic transition temperatures of $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ are gradually suppressed upon Co or Ni doping. A small amount of Co or Ni doping results in a significant increase of the coercive field. In particular, Co doping tunes the crystals from ferromagnetism to antiferromagnetism and then to the spin-glass state, while Ni doping tunes the crystals from ferromagnetism to spin-glass states. The strong doping-dependent magnetic properties suggest that $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ has great potential for spintronic applications.

We performed nuclear magnetic resonance studies on a kagome antiferromagnet ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\mathrm{Br}}_{1-x}{\left(\mathrm{OH}\right)}_x\right]$. No significant NMR spectral broadening is found in the Br center peak from 1 K down to 0.05 K, indicating absence of static antiferromagnetic ordering. In contrast to signatures of dominant 2D kagome antiferromagnetic fluctuations at temperature above 30 K, both the Knight shift $K_{\mathrm{n}}$ and the spin-lattice relaxation rate $1/T_1$ increase when the sample is cooled from 30 K to 8 K, which can be attributed to the scattering of spin excitations by strong nonmagnetic impurities. Unusually, a hump is observed in $K_{\mathrm{n}}$ and $1/T_2$ close to 2 K (far below the exchange energy), which indicates the existence of excitations with a large density of states close to zero energy. These phenomena are reproduced by a mean-field simulation of the Heisenberg model with bond-dependent exchange interactions, where the sign fluctuations in the spinon kinetic terms caused by impurities result in localization of spinons and an almost flat band close to the Fermi energy.

We study impurity effects in the spin nematic phase of the $S=1/2J_1\text{−}{J}_2$ frustrated spin chain under an external magnetic field by using the infinite density matrix renormalization group and bosonization. It is found that local magnetization almost saturates around the impurity, and the entanglement entropy nearly vanishes at the corresponding bonds, not only when the magnetic interactions near the impurity are weakened but also when they are strengthened compared to those in the bulk. Then we examine spin correlations and Friedel oscillations induced by the impurity. The bosonization provides a qualitative understanding of the characteristic behaviors of the magnetization. We also discuss impacts of the impurity on experiments by focusing on NMR spectra.

The possibility to directly measure, in a cold-atom quantum simulator, the von Neumann entropy and mutual information between a site and its environment opens new perspectives on the characterization of the Mott-Hubbard metal-insulator transition, in the framework of quantum information theory. In this work, we provide an alternative view of the Mott transition in the two-dimensional Hubbard model in terms of rigorous quasilocal measures of entanglement and correlation between two spatially separated electronic orbitals, with no contribution from their environment. A space-resolved analysis of cluster dynamical mean-field theory results elucidates the prominent role of the nearest-neighbor entanglement in probing Mott localization: both its lower and upper bounds sharply increase at the metal-insulator transition. The two-site entanglement beyond nearest neighbors is shown to be quickly damped as the intersite distance is increased. These results ultimately resolve a conundrum of previous analyses based on the single-site von Neumann entropy, which has been found to monotonically decrease when the interaction is increased. The quasilocal two-site entanglement recovers instead the distinctive character of Mott insulators as strongly correlated quantum states, demonstrating its central role in the $2d$ Hubbard model.

Metal-insulator transitions in an asymmetric three-component Falicov-Kimball model are investigated within the two-site dynamical mean field theory. The model is obtained from the symmetry breaking of the $SU\left(3\right)$ Hubbard model by imbalanced masses and nonequal local interactions of particle components. The Mott transitions are classified by the change in the number of distinct kinds of doublons across the transition. We observe a different Mott transition between partially localized states in which the particle components (flavors), which form the doublons, are swapped with each other but the number of distinct kinds of doublons is unchanged across the transition. The swap Mott transition occurs as a result of the competition between the Brinkman-Rice and the Falicov-Kimball localizations and the mass imbalance of the mobile particles.

We introduce low-energy effective models for dense configurations of vortices in the Kitaev honeycomb model. Specifically, we consider configurations of vortices in which vortex-free plaquettes form triangular lattices against a vortex-full background. Depending on the vortex density, these “dual” configurations belong to either one of two families classified by translation and inversion symmetry. As a function of a time-reversal symmetry breaking term, one family exhibits gapped phases with even Chern numbers separated by extended gapless phases, while the other exhibits gapped phases with even or odd Chern numbers, separated by critical points. We construct an effective model for each family, determine the parameters of these models by fitting the integrated density of states, and reproduce energy spectra and Chern numbers of the Kitaev honeycomb model. We also derive phase diagrams and determine these models' validity.

The layer Hall effect is a type of Hall effect where electrons on the top and bottom layers deflect in opposite directions. In this paper, we investigate the disorder effects on the layer Hall effect in a magnetic sandwich heterostructure that supports the axion insulator and normal insulator phases. We demonstrate that the layer Hall effect in the axion insulator phase is robust against weak disorder. Most interestingly, we find that the layer Hall effect in the normal insulator phase is significantly enhanced with increasing disorder strength. Theoretically, the disorder-enhanced layer Hall effect at weak disorder is explained by using the Born approximation. Experimentally, we suggest the disorder-enhanced layer Hall effect could be detected by applying a perpendicular electric field.

The spin-resolved thermoelectric transport properties of correlated nanoscale junctions, consisting of a quantum dot/molecule asymmetrically coupled to external ferromagnetic contacts, are studied theoretically in the far-from-equilibrium regime. One of the leads is assumed to be strongly coupled to the quantum dot resulting in the development of the Kondo effect. The spin-dependent current flowing through the system, as well as the thermoelectric properties, are calculated by performing a perturbation expansion with respect to the weakly coupled electrode, while the Kondo correlations are captured accurately by using the numerical renormalization group method. In particular, we determine the differential and nonequilibrium Seebeck effects of the considered system in different magnetic configurations and uncover the crucial role of spin-dependent tunneling on the device performance. Moreover, by allowing for the spin accumulation in the leads, which gives rise to finite spin bias, we shed light on the behavior of the nonequilibrium spin Seebeck effect. In particular, we predict new sign changes of the spin-resolved Seebeck effect in the nonlinear response regime, which stem from the interplay of exchange field and finite voltage and temperature gradients.

We investigate the Goos-Hänchen shifts in reflection for a light beam within a graphene structure utilizing the Fizeau drag effect induced by its massless Dirac electrons in incident light. The magnitudes of spatial and angular shifts for a light beam propagating against the direction of drifting electrons are significantly enhanced, while shifts for a beam copropagating with the drifting electrons are suppressed. The Goos-Hänchen shifts exhibit augmentation with increasing drift velocities of electrons in graphene. The impact of the incident wavelength on the angular and spatial shifts in reflection is discussed. Furthermore, the study highlights the crucial roles of the density of charged particles in graphene, the particle relaxation time, and the thickness of the graphene in manipulating the drag-affected Goos-Hänchen shifts. This investigation offers valuable insights for efficiently guiding light in graphene structures under the influence of the Fizeau drag effect.