Motivated by the recent discovery of odd-parity multipolar antiferromagnetic order in ${\text{CeRh}}_2{\text{As}}_2$, we examine the coexistence of such translation invariant Kramers' degenerate magnetic states and superconductivity. We show that the presence of such magnetic states generically suppresses superconductivity, whether it be spin-singlet or spin-triplet, unless the magnetic state drives a symmetry-required pair density wave superconducting order. We apply our results to ${\text{CeRh}}_2{\text{As}}_2$, where no pair density wave order appears, and to the loop current order in the cuprates, where such pair density wave superconductivity must appear together with Bogoliubov Fermi surfaces. In the former case, we explain why superconductivity is not suppressed.

Within the Floquet theory of periodically driven quantum systems, we demonstrate that an off-resonant high-frequency electromagnetic field can induce the Lifshitz phase transition in periodical structures described by the one-dimensional repulsive Hubbard model with the nearest- and next-nearest-neighbor hopping. The transition changes the topology of electron energy spectrum at the Fermi level, transforming it from the two Fermi points to the four Fermi points, which facilitates the emergence of the superconducting fluctuations in the structure. Possible manifestations of the effect and conditions of its experimental observability are discussed.

Recent experiments have reported that depositing K atoms onto the surfaces of nonsuperconducting FeSe thin films can not only transform them into superconductors but also obtain a domelike relation between the superconducting transition temperature ($T_{\text{c}}$) and the K coverage ($K_{\text{c}}$). To elucidate the mechanism underlying the domelike dependence of $T_{\text{c}}$ on $K_{\text{c}}$ in K-coated FeSe (K/FeSe) films, we have studied the electronic and magnetic properties of the K/FeSe films at $K_{\text{c}}=0.125$, 0.25, and 0.5 ML [1 monolayer (ML) is defined as the areal density of the topmost Se site] based on the first-principles electronic structure calculations. Our calculations show that there are two antiferromagnetic (AFM) states being energetically quite close to each other regardless of the value of $K_{\text{c}}$, indicating that there may exist strong magnetic fluctuations in K/FeSe. On the other hand, it is worth noting that the differential charge and spin densities between the two AFM states at three $K_{\text{c}}$'s demonstrate that both the charge density redistributions around Se atoms and the spin density redistributions around Fe atoms have the domelike evolution with $K_{\text{c}}$, which coincide with the observed behavior of superconducting $T_{\text{c}}$. Furthermore, we find that the densities of states at the Fermi level $\left[N\left(E_{\text{F}}\right)\right]$ in these two AFM states also have a domelike dependence on $K_{\text{c}}$. Apart from helping us understand the superconducting mechanism in the K/FeSe system, these results also provide a different perspective for exploring the superconductivities in other FeSe-based superconductors.

Creating heterostructures with graphene/graphite is a practical method for charge-doping $\alpha \text{−}{\mathrm{RuCl}}_3$, but not sufficient to cause the insulator-to-metal transition. In this study, detailed scanning tunneling microscopy/spectroscopy measurements on $\alpha \text{−}{\mathrm{RuCl}}_3$ with various lattice deformations reveal that both in-plane and out-of-plane lattice distortions may collapse the Mott gap in the case of monolayer $\alpha \text{−}{\mathrm{RuCl}}_3$ in proximity to graphite, but have little impact on its bulk form alone. In the Mott-Hubbard framework, the transition is attributed to the lattice-distortion-facilitated substantial modulation of the electron correlation parameter. Observation of the orbital textures on a highly compressed monolayer $\alpha \text{−}{\mathrm{RuCl}}_3$ flake on graphite provides valuable evidence that electrons are efficiently transferred from the heterointerface into $\mathrm{C}\mathrm{l3}p$ orbitals under the lattice distortion. It is believed that the splitting of Ru $t_{2g}$ bands within the trigonal distortion of Ru-Cl-Ru octahedra bonds generated the electrons' transfer pathways. The increase of the $\mathrm{C}\mathrm{l3}p$ states enhances the hopping integral in the Mott-Hubbard bands, resulting in the Mott transition. These findings suggest a different route for implementing the insulator-to-metal transition upon doping in $\alpha \text{−}{\mathrm{RuCl}}_3$ by deforming the lattice in addition to the formation of the heterostructure.

Twisted bilayer graphene (TBG) is known for exhibiting highly correlated phases at magic angles due to the emergence of flat bands that enhance electron-electron interactions. The connection between magic angles and the quantum Hall effect remains a topic of ongoing research. In the TBG chiral model, electronic wave function properties depend on a single parameter ($\alpha$), inversely proportional to the relative twist angle between the two graphene layers ($\theta$), which includes the interlayer interaction strength. In previous studies, as the twist angles approached small values, strong confinement and a convergence to coherent Landau states were observed. However, the origin of these phenomena remained elusive. In this paper, we explore flat band electronic modes, revealing that flat band states exhibit self-duality; they are coherent Landau states in reciprocal space and exhibit minimal dispersion, with standard deviation ${\sigma }_k=\sqrt{3\alpha /2\pi }$ as $\theta \to 0$. Subsequently, by symmetrizing the wave functions and considering the squared TBG Hamiltonian, the strong confinement observed in the $\theta \to 0$ limit is explained. This confinement arises from the combination of the symmetrized squared norm of the moiré potential and the quantized orbital motion of electrons, effectively creating a quantum well. The ground state of this well, located at non-high-symmetry spots, corresponds to a Landau level. Furthermore, we demonstrate that the problem is physically analogous to an electron attached to a non-Abelian $\text{SU}\left(2\right)$ gauge field with underlying $C_3$ symmetry. In regions of strong confinement, the system can be considered Abelian, aligning with the picture of a simple harmonic oscillator. This allows us to define a magnetic energy in which the important role of the wave function parity and gap closing at nonmagic angles is revealed. Finally, we investigate the transition from the original non-Abelian nature to an Abelian state by artificially changing the pseudomagnetic vector components from an $\text{SU}\left(2\right)$ to a U(1) field, which alters the sequence of magic angles. An experimental proposal is made to measure such effects.

The domain walls between AB- and BA-stacked gapped bilayer graphene have garnered intense interest as they host topologically protected, valley-polarized transport channels. The introduction of a twist angle between the bilayers and the associated formation of a moiré pattern has been the dominant method used to study these topological channels, but heterostrain can also give rise to similar stacking domains and interfaces. Here, we theoretically study the electronic structure of a uniaxially heterostrained bilayer graphene. We discuss the formation and evolution of interface-localized channels in the one-dimensional moiré pattern that emerges due to the different stacking registries between the two layers. We find that a uniform heterostrain is not sufficient to create one-dimensional topological channels in biased bilayer graphene. Instead, using a simple model to account for the in-plane atomic reconstruction driven by the changing stacking registry, we show that the resulting expanded Bernal-stacked domains and sharper interfaces are required for robust topological interfaces to emerge. These states are highly localized in the AA- or SP-stacked interface regions and exhibit differences in their layer and sublattice distribution depending on the interface stacking. We conclude that heterostrain can be used as a mechanism to tune the presence and distribution of topological channels in gapped bilayer graphene systems, complementary to the field of twistronics.

We study the second-order optical response of Weyl semimetals in the presence of a magnetic field. We consider an idealized model of a perfectly linear Weyl node and use the Kubo formula at zero temperature to calculate the intrinsic contribution to photocurrent and second harmonic generation conductivity components. We obtain exact analytical expressions applicable at arbitrary values of frequency, chemical potential, and magnetic field. Our results show that finite magnetic field significantly enhances the nonlinear optical response in semimetals, while magnetic resonances lead to divergences in nonlinear conductivity. In realistic systems, these singularities are regularized by a finite scattering rate but result in pronounced peaks which can be detected experimentally, provided the system is clean and interactions are weak. We also perform a semiclassical calculation that complements and confirms our microscopic results at small magnetic fields and frequencies.

Controlling the metal-insulator transition in graphene-based material is a crucial topic as it directly impacts its potential applications. Inspired by recent experiments, we study the effects of doping and bond disorder on the metal-insulator transition in graphene within the Hubbard model on a honeycomb lattice. By using the determinant quantum Monte Carlo method, we first conduct tests on the value of $\langle \text{sign}\rangle$ under various parameters, such as electron density, on-site interactions, temperature, and lattice size, so as to select the appropriate parameters to alleviate the impact of the sign problem. Given the knowledge that bond disorder can lead to a metal-insulator transition, our study has revealed, after ruling out the influence of size effects, that the critical strength of disorder increases as the electron density decreases while decreasing as the on-site interactions increase. Furthermore, we compare our results with experimental data and conclude that, in actual graphene materials, the localization effect induced by doping plays a dominant role, resulting in an insulating phase.

Typically, edge states in graphene are known to exist solely along zigzag edges. However, in this paper, we present a theoretical discovery of edge states along armchair edges in graphene under shear strain. This phenomenon arises from shear strain causing a separation between two inequivalent Dirac cones in the Brillouin zone (BZ) along the zigzag direction. Consequently, these armchair edge states appear as flat bands, connecting the two Dirac points at the two edges of armchair graphene nanoribbons (AGNRs). The length of these flat bands in the BZ and the penetration depth of the edge states are directly and inversely proportional to the strain, respectively. In monolayer AGNRs, possible magnetic configurations of flat bands resulting from electron-electron interactions are investigated. The edge-to-edge antiferromagnet (AFM) ground state is found in neutral AGNRs, while the AFM to ferromagnet (FM) transition can occur and be controlled by the strain in low-doped AGNRs. In gapped bilayer AGNRs, the armchair edge states evolve into quantum valley Hall edge states (QVHESs), which significantly improves the conductivity of QVHESs at realistic imperfect sample edges. These armchair edge states present a promising and tunable platform for exploring topological edge states in graphene.

The observation of the magnon Hall effect (MHE) has relied solely on the challenging measurement of the thermal Hall conductivity. Here, we report a highly sensitive electrical Seebeck contrast method for the observation of MHE in ${\mathrm{Lu}}_2{\mathrm{V}}_2{\mathrm{O}}_7$/heavy metal heterostructures, which is highly desirable for the exploration of new MHE materials and their applications. Using measuring wires with very different Seebeck coefficients, we established a general method that can separate contributions (e.g., MHE) that generates a lateral temperature drop, from those [e.g., anomalous Nernst effect (ANE) and spin Seebeck effect (SSE)] that generate a lateral electric field. We show that a suitable heavy metal overlayer can eliminate the inherent ANE and SSE signals from the semiconducting ${\mathrm{Lu}}_2{\mathrm{V}}_2{\mathrm{O}}_7$. The MHE in ${\mathrm{Lu}}_2{\mathrm{V}}_2{\mathrm{O}}_7$ is quasi-isotropic among crystals with different orientations. In addition to the previously reported transverse MHE under an in-plane temperature gradient, we have uncovered longitudinal MHE under an out-of-plane temperature gradient.

We develop a theory of nonreciprocal current-voltage (I-U) characteristics in noncentrosymmetric superconductor-normal metal-superconductor junctions. We show that at small voltages the nonreciprocal features of the I-U characteristics can be expressed entirely in terms of the dependence of the nonreciprocal part of the quasiparticle density of states in the normal metal part of the junction on the order parameter phase difference $\chi$ across the junction. The amplitude of the nonreciprocity in this regime is proportional to the inelastic quasiparticle relaxation time ${\tau }_{in}$, and can be much larger than that in normal materials, where it is proportional to the elastic relaxation time ${\tau }_{el}$. At low bias the I-U characteristics possess additional symmetry not present in normal conductors; they remain invariant under simultaneous reversal of current, voltage, and the magnetic field.

We predict the plasmon instability associated with losses in hydrodynamic graphene with a drift-current bias. The instability appears even in a single-layer graphene and becomes stronger for greater losses in graphene in hydrodynamic regime but disappears in the lossless case. The unstable plasmon mode vanishes for zero drift velocity instead of transforming into any plasmon mode existing in graphene without carrier drift. The dissipative instability occurs for any finite drift velocity but the instability increment decreases down to zero for vanishing carrier drift velocity. The strongest instability develops for codirected carrier drift and plasmon propagation directions.

Plasmonic mode conversion is an important topic for realizing the coupling between conventional optical and plasmonic waveguides, and between plasmonic waveguides. However, the switchable mode conversion between the symmetric and the antisymmetric modes propagating along metal slab waveguides, which are among well-known prototypes of surface plasmon polariton (SPP) modes, has never been reported, to our knowledge. In this paper, we suggested the conversion between the symmetric and the antisymmetric modes by introducing a gyration-managed metal slab waveguide link with the zero-averaged gyration. The symmetric (antisymmetric) mode can be converted to the antisymmetric (symmetric) mode with ultrahigh conversion efficiency more than $98\%$.

We develop Green's function formalism to describe continuous multilayered quasi-one-dimensional setups described by piecewise constant single-particle Hamiltonians. The Hamiltonians of the individual layers are assumed to be quadratic polynomials in the momentum operator with matrix-valued (multichannel) coefficients. This, in particular, allows one to study transport in heterostructures consisting of multichannel conducting, superconducting, or insulating components with band structures of arbitrary complexity. We find a general expression for the single-particle Green's function of the combined setup in terms of the bulk (translationally invariant) Green's functions of its constituents. Furthermore, we provide the expression for the global density of states of the combined system and establish the bound state equation in terms of bulk Green's functions. We apply our formalism to investigate the spectrum and current-phase relations in ordinary and topological Josephson junctions, additionally showing how to account for the effects of static disorder and local Coulomb interaction.

Magnetic skyrmions, vortex-like spin textures possessing remarkable topological electron-magneto properties, have emerged as promising candidates for information storage and processing in future spintronic devices. Helicity, which characterizes the rotational sense of the spin swirl, represents a crucial degree of freedom for encoding information in magnetic skyrmions. Traditionally, states with one and two helicities have been established for skyrmions in chiral and dipolar/frustrated magnets, respectively. In this study, we explore the helicity diversity of dipolar skyrmions in centrosymmetric magnets by extending our investigation to three-dimensional uniaxial magnetic systems. Combining numerical simulations, we demonstrate that the inclusion of additional spin twists along the depth dimension expands the twofold helicity degeneracy to fourfold and potentially beyond. Our findings not only provide insights into the spin models of dipolar skyrmions but also promote the development of topological spintronic devices, leveraging helicity as a key parameter.

Fast relaxation, a locally dynamic activation, universally occurs in metallic glasses below room temperature. Despite much attention, its structural origin has barely been solved and remains mysterious. In this work, the dynamic mechanical relaxations of a typical Zr-based metallic glass with different structural states are systematically studied from 135 to 748 K. We find that the single-peak (${\beta }^{\prime }$) fast relaxation in the annealed glass splits into two distinct peaks (γ and ${\beta }^{\prime }$) by multiple-pulse laser shocks, and this dynamics splitting will vanish after re-annealing. Slight structural rejuvenation of the laser-shocked sample is detected by thermodynamic measurements. Structural characterizations further reveal that the laser shocks lead to an increase in the edge-sharing medium-range orders (MROs), which is then recovered by re-annealing. The one-to-one changes in relaxation dynamics and atomic structures provide convincing evidence that the fast relaxation originates from the excitation of MRO structures, and its splitting is due to the reconstruction of MROs. We also find that the split fast relaxations contribute to the room-temperature plasticity of the studied glasses.