The equal- and opposite-spin pairing correlations in silicene-based ferromagnet/ferromagnet/superconductor (F/F/SC) and F/F/SC/F/F junctions controlled by electric field are investigated. The noncollinear magnetization is a necessary condition for generating the novel Andreev reflection (NAR), novel crossed Andreev reflection (NCAR), and spin-flip elastic cotunneling (SFEC) processes, due to the spin-flip scattering at the F/F interface. Different from conventional scattering, the strong signal of spin-flip scattering process is distributed in finite polar and azimuthal angle spaces. A switch effect between conventional AR (CAR) and NAR (NCAR) can be realized in the F/F/SC (F/F/SC/F/F) junction by tuning the exchange and electric fields. The EC conductance is symmetric about the azimuthal angle $\phi =\pi$, whereas the spin-flip scattering breaks the symmetry leading to an asymmetrical SFEC conductance. Different from spin polarization, the valley polarization for both the conventional AR and NAR can be tuned from 100% to $-100$% by reversing the directions of not only exchange field but also electric field. Moreover, the more the exchange energy approaches zero (Fermi energy), the larger the negative maximum value of the nonlocal (local) magnetoresistance becomes.

A composite impurity in a metal explores different configurations, where its net magnetic moment may be screened by the electrons in the host. An interesting example is the two-stage Kondo (TSK) system where screening sets in with successively smaller energy scales. In contrast, the impurities may prefer a local singlet disconnected from the metal. This competition is decided by fine-tuning the couplings in the system, as has been studied before. A double quantum dot T-shape geometry, where a hanging dot is connected to current leads only via another dot, represents a flexible system in which these different regimes can be explored experimentally. It has been difficult, however, to clearly differentiate the two regimes. Here we provide a prescription to better identify the regime where the TSK occurs in such double dot geometry. The TSK regime requires a balance of the ratio $t_{01}/{\mathrm{\Gamma }}_0$ between the interdot coupling ($t_{01}$) and the coupling of the QD connected to the Fermi sea (${\mathrm{\Gamma }}_0$). Above a certain value of this ratio, the system crosses over to a molecular regime, where the quantum dots form a local singlet and no Kondo screening occurs. Here we establish that there is a region in the $t_{01}–{\mathrm{\Gamma }}_0$ parameter space where a pure TSK regime occurs, i.e., where the properties of the second Kondo stage can be accurately described by a single impurity Anderson model with effective or renormalized parameters. By examining the magnetic susceptibility of the hanging QD, we show that a single parameter, ${\mathrm{\Gamma }}_{\mathrm{eff}}$, can accurately simulate this susceptibility. This effective model also provides the hanging QD spectral function with great accuracy in a limited range of the $t_{01}–{\mathrm{\Gamma }}_0$ parameter space, thus defining the region where a true TSK regime occurs. We also show that in this parameter range, the spin correlations between both quantum dots show a universal behavior. Our results may guide experimental groups to choose parameter values that will place the system either in the TSK regime or in the crossover to the molecular regime.

Two-dimensional materials present a distinctive platform for investigating the interplay between magnetism and topology. In this study, we explore the bilayer form of the 2D honeycomb ${\mathrm{V}}_2{\mathrm{O}}_3$ monolayer, identified as a promising candidate for a quantum anomalous Hall insulator, and propose topological phases for this bilayer system. Our findings indicate that ${\mathrm{V}}_2{\mathrm{O}}_3$ bilayers are energetically stable in the AB-stacking configuration with antiferromagnetic ordering. The antiferromagnetic state, observed in both AA- and AB-stacking configurations, yields a quantum spin Hall state with a ${\mathbb{Z}}_2$ invariant of 1. Conversely, the ferromagnetic state results in a quantum anomalous Hall state with a Chern number $(C=2)$. Significantly, the stable antiferromagnetic state is likely attributed to direct exchange interactions between adjacent V atoms in different layers. These results highlight the tunable topological properties of the ${\mathrm{V}}_2{\mathrm{O}}_3$ bilayer system and provide valuable insights for the design and manipulation of magnetic topological materials in two-dimensional systems.

The density of states and differential entropy per particle are analyzed for Dirac-like electrons in graphene subjected to a perpendicular magnetic field and an in-plane electric field. For comparison, the derived density of states is contrasted with the well-known case of nonrelativistic electrons in crossed magnetic and electric fields. The study considers ballistic electrons and also includes the effect of small impurity scattering. In the latter case, the limit of zero magnetic field and the so-called collapse of Landau levels in graphene are examined analytically. By comparing the results with numerical calculations on graphene ribbons, we demonstrate that the Landau state counting procedure must be modified for Dirac-like electrons, leading to a fields-dependent Landau level degeneracy factor. Additionally, it is shown that peaks in the differential entropy arise from the dispersionless surface mode localized at the zigzag edges of the ribbon.

Coupled spin evolution and tunneling together with the relaxation and decoherence effects are studied for the double quantum dot formed in a semiconductor nanowire and driven by the periodic electric field. Such structure represents a model of the spin and charge subsystems interacting via the strong spin-orbit coupling. It is found that at certain regimes the combination of fast relaxation in the coordinate channel with the slower relaxation in the spin channel leads to the promising combination of fast spin manipulation and slow spin relaxation, locking the flipped spin in an excited state in one of the dots for a sufficiently long time. The predicted effect is maintained for a wide range of relaxation times and driving amplitudes both for the coordinate and the spin channels and is also observed in higher subharmonics which require lower driving frequencies.

This Letter presents the design and measurement of two different metastructures based on a complementary metallic plate array spoof surface plasmon polariton structure. The voltage transmitted through the structures was measured with respect to the frequency and angle of incidence of the wave impinging on the surface for both transverse magnetic (TM)-polarized and transverse electric (TE)-polarized waves. The results were then compared with simulation results obtained through Floquet analysis with periodic boundaries. The measurement results are in good agreement with the simulation results, confirming that the shift in the resonance frequency of the structure depends on the angle of incidence and polarization of the impinging wave, which indicates that this angle dependence dataset provides direct experimental information on the band structure achievable by these metasurfaces.

The Yang-Lee edge singularity is an intriguing critical phenomenon characterized by nonunitary field theory. However, its experimental realization for interacting many-body systems remains elusive. We show that Yang-Lee edge singularities, regarded as many-body exceptional points, can be observed using both the self-normal and the associated-biorthogonal Loschmidt echoes, leveraging the advantages of nonunitary dynamics in non-Hermitian systems. The Loschmidt echoes are demonstrated to display unitary dynamics in the $\mathcal{PT}$-symmetric regime but exhibit nonunitary dynamics in the $\mathcal{PT}$-symmetry-broken regime, leading to a sharp change near an exceptional point. We hereby identify exceptional points in both the non-Hermitian transverse-field Ising model and the Yang-Lee model, and determine the critical exponent that is consistent with nonunitary conformal field theory. This paper provides a direct observation of Yang-Lee edge singularities in non-Hermitian many-body systems arising from nonunitary dynamics.

With the goal of creating an in-plane (IP) uniaxial anisotropy system, we deposited a thickness series of epitaxial $\mathrm{Co}\left(10\overline{1}0\right)$ films grown on Si(110) substrates with Ag(110) and Cr(211) buffer layers by magnetron sputtering. However, quantifying the IP magnetic anisotropy using ferromagnetic resonance measurements revealed a much more complex behavior than expected for a simple uniaxial system like hexagonally close-packed (hcp) Co. To understand the experimental results, an in-depth x-ray diffraction analysis of the film structure was performed. Even at a thickness of 100 nm, it revealed an anisotropic strain in the Co films, mainly within the Co basal plane, while the $c$ axis remained mostly unaffected. Calculations show that such unrelaxed strain induces a significant magnetoelastic anisotropy, which counteracts the magnetocrystalline one and, as a result, reduces the overall effective anisotropy. A detailed analysis revealed that mainly the compressive strain along the $\mathrm{Co}\left[10\overline{1}0\right]$ out-of-plane direction is responsible for the observed magnetoelastic anisotropy, while the tensile strain along the $\mathrm{Co}\left[\overline{1}2\overline{1}0\right]$ IP direction only plays a minor role.

Recent years have seen the concept of global symmetry extended to noninvertible (or categorical) symmetries, for which the composition of symmetry generators is not necessarily invertible. Such noninvertible symmetries lead to a generalization of the standard Landau paradigm. In this work, we substantiate this framework by providing a $(1+1)\mathrm{d}$ lattice model, whose gapped phases and phase transitions can only be explained by symmetry breaking of noninvertible symmetries.

We perform low-frequency ac first- and second-harmonic resistance measurements and dc $I-V$ measurements on bulk FeSe crystals in a temperature range between 1.8 and 150 K and in magnetic field up to 14 T. We observe considerable second-harmonic resistance, indicative of nonreciprocal charge transport, in some samples. By examining the correlation between contact resistances and second-harmonic signals, we conclude that the second-harmonic resistance is not due to the genuine nonreciprocal transport effect, but is caused by joule heating at a current contact through the thermoelectric effect. Our conclusion is consistent with a recent preprint (Nagata et al., arXiv:2409.01715), in which the authors reported a zero-field superconducting diode effect in devices fabricated with FeSe flakes and attributed it to the thermoelectric effect.

Topological magnonics opens avenues for robust, reconfigurable, and scalable magnon-based spintronic devices. In this paper, we propose a Floquet no-go theorem for magnetically ordered systems, which identifies forbidden auxiliary hoppings induced by circularly polarized laser light. Based on this theorem and perturbation theory, we establish a set of rules for engineering topological magnons from massless Dirac magnons. We demonstrate the realization of topological magnons in both non-Bravais lattice ferromagnets and Bravais lattice antiferromagnets, along with calculations of their magnon band topological properties and thermal Hall conductivities. We discuss potential material candidates for experimental realization of our results. Our research establishes a systematic framework for engineering topological magnons in magnetically ordered systems, thereby expanding the search scope for topological magnon materials.

We present a detailed mean-field study to address the fundamental discrepancy in the ground state magnetization of ${\mathrm{Sr}}_2{\mathrm{CoO}}_4$ (SCO). In contrast to the ferromagnetic metallic ground state obtained from density functional theory (DFT), $\mathrm{DFT}+U$ gives three ferromagnetic solutions converging to integer moment values (1, 2, and 3 ${\mu }_B/\mathrm{f}.\mathrm{u}.$) over a range of $U$. Interestingly, two of the solutions are found to exhibit half-metallicity with correspondingly $S=1/2$ and $S=3/2$ spin states. The half-metallic ferromagnetic state with $S=3/2$ is found to be the ground state solution for SCO. Co atoms show large deviation from the formal $+4$ oxidation state indicating the presence of strong covalency effects. Our results suggest a plausible metal to half-metal phase transition around $U\left(J\right)=4.4 \left(1.16\right) \mathrm{eV}$. The Fermi surface study shows gradual collapse in states leading to half-metallicity suggesting k dependence of effective U around the critical region. Surprisingly, in the presence of spin-orbit coupling an unexpectedly large orbital moment $(L_z=0.6)$ is noted in SCO putting it among the class of $3d$-based transition metal compounds exhibiting pronounced orbital magnetization. The calculations give a large magnetocrystalline anisotropy energy (MAE) of $\sim 48$ meV. The large orbital magnetic moment contribution and MAE, in the presence of strong correlation effects, provide a better interpretation of experimental magnetization observed in SCO.

The Franck-Condon principle and Condon approximation are key to understanding optical transitions. This study uses first-principles calculations to simulate luminescence and absorption line shapes of hexavalent Mn ions in alkali-metal sulfates, revealing a significant Herzberg-Teller effect in this electric-dipole allowed transition. These findings show the limitations of the Condon approximation and the need for more sophisticated approaches to accurately simulate optical phenomena.

We derive the macroscopic charge and current densities of a Chern insulator initially occupying its electronic ground state as it responds to a finite-frequency electric field; we use a previously developed formalism based on microscopic polarization and magnetization fields in extended media. In a topologically trivial insulator, our result reduces to the familiar expression for the induced current density in linear response obtained from a Kubo analysis. However, for a Chern insulator, we find an extra “topological” term involving the (first) Chern number associated with the occupied bands, encoding the quantum anomalous Hall effect in the presence of a frequency-dependent electric field. While an analogous term has been introduced in the “modern theories of polarization and magnetization” for the linear response of finite-sized systems to static electric fields, our expression is valid for bulk Chern insulators in the presence of both static and finite-frequency electric fields, being derived analytically from a microscopic treatment of the electronic degrees of freedom, and can be generalized in a straightforward way to describe the response of a Chern insulator to electromagnetic fields that are not only frequency-dependent but also spatially inhomogeneous.

The formation and growth of ice particles, particularly on the surfaces of spherical water droplets, bear profound implications for localized weather systems and global climate. Herein, we develop a theoretical framework for ice nucleation on minuscule water droplets, establishing that $10–5000\mathrm{nm}$ droplets can considerably increase in volume, making a substantial contribution to ice formation within mist, fog, or even cloud systems. We reveal that the Casimir-Lifshitz (van der Waals) interaction within these systems is robust enough to stimulate both water and ice growth on the surfaces of ice-cold spherical water droplets. The significant impacts and possible detectable phenomena from the curvature are demonstrated.

Bound states in the continuum (BICs), which are localized waves within a continuous spectrum of radiating waves, have garnered considerable attention due to their counterintuitive physical properties. However, selectively exciting these bound states from the continuum remains challenging because of their degenerate eigenenergy. In this work, we propose a method to accurately excite high-order topological BICs (TBICs) using supersymmetric (SUSY) structures. By adiabatically transforming the SUSY partner to the original lattice, TBICs can be perfectly excited with simple single-site excitation. We experimentally verify our strategy in photonic waveguides at telecommunication wavelengths, demonstrating efficient excitation and the existence of TBICs across a broadband. Our work highlights the superior capability of SUSY in regulating optical BIC modes, suggesting possibilities for exploring BICs in higher-dimensional lattices.

Recently, a novel collinear magnet, i.e., the altermagnet (AM), with spin-splitting energy band and zero net magnetization has attracted great interest due to its potential spintronic applications. Here, we demonstrate AM-like phases in a microscopic Kondo lattice (KL) model with an alternating next-nearest-neighbor hopping (NNNH). Such alternating NNNH takes nonmagnetic atoms, neglected in usual antiferromagnetism study, into account when encountering real-life candidate AM materials. With the framework of fermionic parton mean-field theory, we find three different ground states for the half-filling KL: (i) a $d\text{−}\mathrm{wave}$ AM state; (ii) a coexistent phase with both $d\text{−}\mathrm{wave}$ AM and intrinsic Kondo screening effect; (iii) a Kondo insulator. The AM-like states are characterized by their spin-splitting quasiparticle bands, Fermi surface, spin-resolved distribution function, and conductivity. It is suggested that the magnetic quantum oscillation, scanning tunneling microscopy, and charge transport measurement can detect those AM-like phases. We hope the present work may be useful for exploring AM-like phases in $f\text{−}\mathrm{electron}$ compounds such as CeNiAsO and ${\mathrm{Ce}}_4{X}_3$ $(X=\mathrm{As}, \mathrm{Sb}, \mathrm{Bi})$.

Various properties of interlayer excitons in double-layer transition metal dichalcogenide quantum dots are analyzed using a low-energy effective Hamiltonian with Coulomb interaction. We analytically solve the single-particle Hamiltonian with and without a magnetic field, then present the electron-hole pairing features of interlayer excitons by employing the exact-diagonalization technique, where the electron and hole are located in two layers, respectively. In a magnetic field, the Landau-level gap, as well as the electron-hole separation of an exciton, varies nonmonotonously as the interlayer distance increases, which is attributed to the pseudo-spin-orbit coupling that also leads to the emergence of topological nontrivial pseudospin textures in the exciton states. We examine the influence of different materials in quantum dots stacking on the exciton states, comparing their impact to variations in layer distances and quantum dot sizes. We further explore two interacting interlayer excitons numerically. The binding energy is significantly enhanced by the exchange interaction when the two electrons have different spins. The optical absorption spectra from the ground state to low-lying excited states reveal distinct behaviors for different interlayer excitons, which can be utilized to distinguish the spin of electrons in excitons. Our results highlight the potential for controlling interlayer excitons and applications of optical devices in a magnetic field and tunable layer distance.