According to spin Seebeck effect, a thermal spin current will be produced when a temperature gradient is applied to the metallic ferromagnet. Similar to the electrical spin transfer torque (ESTT) induced by spin-polarized current, there is also a thermal spin transfer torque (TSTT) caused by the thermal spin current, which can be attributed to the s-d interaction between the conduction electrons and the local magnetization. In this paper, the generalized analytical expressions of thermal spin current and TSTT are derived based on the spinor Boltzmann equation (SBE) under the local equilibrium approximation. This generalized TSTT has different terms compared to the previous phenomenological form, and the phenomenological coefficients can be determined theoretically within our framework. Combined with the SBE under the applied electric field and temperature gradient, we solve the Landau-Lifshitz-Gilbert-Levy equation to study the domain wall (DW) motion driven by the ESTT and TSTT. We investigated the temperature-dependent DW motion, the total spin torque, and TSTT in permalloys. We found that the velocity of the DW can be promoted by increasing temperature and temperature gradient, which provide a path to effectively utilize the Joule heating in spintronics devices.

A domain wall separating two different topological phases of the same crystal can support the propagation of backscattering-immune guided waves. In valley-Hall and quantum-Hall crystal waveguides, this property stems from symmetry protection and results from a topological transition at a Dirac point. Since an initially closed band gap has to open, the guidance bandwidth remains limited compared to that of wide band gap crystals. When a glide-symmetric dislocation is introduced in a 2D crystal, we show that a pair of wide-bandwidth, single-mode, and symmetry-protected guided waves appear in the bulk band gap. The 2D Zak phase changes by $\pi$ on either side of the interface, providing a topological invariant protected by glide-reflection symmetry at the X point of the Brillouin zone. A demonstration experiment is performed with acoustic waves in water, at ultrasonic frequencies, and shows the continuous tuning of transmission as a function of the glide parameter. The concept further extends to other types of waves, including the case of elastic waves in solids, but also of optical and electromagnetic waves.

We study the stroboscopic dynamics of a periodically driven finite Rydberg chain with staggered ($\mathrm{\Delta }$) and time-dependent uniform $\left[\lambda \right(t\left)\right]$ detuning terms using exact diagonalization. We show that at intermediate drive frequencies (${\omega }_D$), the presence of a finite $\mathrm{\Delta }$ results in violation of the eigenstate thermalization hypothesis (ETH) via clustering of Floquet eigenstates. Such clustering is lost at special commensurate drive frequencies for which $\hslash {\omega }_d=n\mathrm{\Delta }$ ($n\in Z$) leading to restoration of ergodicity. The violation of ETH in these driven finite-sized chains is also evident from the dynamical freezing displayed by the density-density correlation between Rydberg excitations at even sites of the chain for specific ${\omega }_D$. Such a correlator exhibits stable oscillations with perfect revivals when driven close to the freezing frequencies for initial all spin-down ($|0\rangle$) or Neel ($|{\mathbb{Z}}_2\rangle$, with up spins on even sites) states. In contrast, for the $|{\overline{\mathbb{Z}}}_2\rangle$ (time-reversed partner of $|{\mathbb{Z}}_2\rangle$) initial state, we find complete absence of such oscillations leading to freezing for a range of ${\omega }_D$; this range increases with $\mathrm{\Delta }$. We also study the properties of quantum many-body scars in the Floquet spectrum of the model as a function of $\mathrm{\Delta }$ and show the existence of mid-spectrum scars at large $\mathrm{\Delta }$ which do not have overlap with either $|0\rangle$ or $|{\mathbb{Z}}_2\rangle$ states. We supplement our numerical results with those from an analytic Floquet Hamiltonian computed using Floquet perturbation theory which allows us to provide qualitative analytical explanations of the above-mentioned numerical results.

We report on the evolution of the spin-wave spectrum under structural disorder introduced intentionally into a one-dimensional magnonic quasicrystal. We study theoretically a system composed of ferromagnetic strips arranged in a Fibonacci sequence. We considered several stages of disorder in the form of phasonic defects, where different rearrangements of strips are introduced. By transition from the quasiperiodic order towards disorder, we show a gradual degradation of spin-wave fractal spectra and closing of the frequency gaps. In particular, the phasonic defects lead to the disappearance of the van Hove singularities at the frequency gap edges by moving modes into the frequency gaps and creating new modes inside the frequency gaps. These modes disperse and eventually can close the gap, with increasing disorder levels. The work reveals how the presence of disorder modifies the intrinsic spin-wave localization existing in undefected magnonic quasicrystals. The paper contributes to the knowledge of magnonic Fibonacci quasicrystals and opens the way to study of the phasonic defects in two-dimensional magnonic quasicrystals.

The kagome lattice antiferromagnet ${\mathrm{Mn}}_3\mathrm{Ge}$ has a local hexagonal symmetry with a ${120}^{\circ }$ ordered ground state. This noncollinear ground state engenders a strong anomalous Hall response. The main goal of this work is to understand the effect of strain on this response. We derive an effective model for the Hall vector which functions as our order parameter. Using this model we show how both intraplanar and interplanar strains can be used to switch the sign of the Hall response at a constant magnetic field. Further, we also investigate the effect of this strain on the spin-wave band gaps and show that strain can be used to effectively manipulate them, which can be used to tune the magnon responses in this system.

Interest in antiferromagnetic (AFM) spintronics has been greatly stimulated by both the complex interplay between antiferromagnetism and band topology and the electrical switching of exotic properties they give rise to. However, the topological phase transitions are usually associated with magnetic transitions where the AFM ordering may be heavily deformed and limit their promising applications. Here, by first-principles calculations and a tight-binding model, we show that an electrically controlled topological phase transition with robust AFM ordering is possible in a honeycomb lattice, and remarkably the long-awaited AFM quantum anomalous Hall effect is obtained. The calculated spin Chern number and Chern number for a two-dimensional AFM topological insulator and AFM Chern insulator are, respectively, ${\mathcal{C}}_{\mathcal{S}}=1$ and $\mathcal{C}=1$, which are further explicitly confirmed by the corresponding helical and chiral edge states. Moreover, we identify intrinsic AFM $X_3\mathrm{Mn}{\mathrm{N}}_3$ $(X=\mathrm{Sr},\mathrm{Ba})$ bilayers as probable candidates for the experimental realization of the proposed phenomenon, and unexpectedly point out that the valley polarization of AFM $X_3\mathrm{Mn}{\mathrm{N}}_3$ is much larger than that of the known ferrovalley systems, indicating the high possibility of innovative applications in AFM spintronics and valleytronics.

We study a quantum many-body variant of the parametric oscillator by investigating the driven sine-Gordon model with a modulated tunnel coupling via a semiclassical truncated Wigner approximation (TWA). We first analyze the parametric resonant regime for driving protocols that retain our model gapped, and compare the TWA to a time-dependent Gaussian variational ansatz (TGVA). We then turn to a drive which closes the gap, resulting in an enhanced energy absorption. While the TGVA approach breaks down in this regime, we can apply TWA to explore the dynamics of the mode-resolved energy density and the higher-order correlations between modes in the prethermal heating regime. For weak driving amplitude, we find an exponentially fast energy absorption in the main resonant mode, while the heating of all remaining modes is almost perfectly suppressed on short timescales. At later times, the highly excited main resonance provides effective resonant driving terms for its higher harmonics through the nonlinearities in the Hamiltonian, and gives rise to an exponentially fast heating in these particular modes. We capture the strong correlations induced by these resonant processes by evaluating higher-order connected correlation functions. Our results can be experimentally probed in ultracold-atomic settings, with parallel one-dimensional quasicondensates in the presence of a modulated tunnel coupling.

The electronic structure and the physical properties of quantum materials can be significantly altered by charge carrier doping and magnetic state transition. Here we report a discovery of a giant and reversible electronic structure evolution with doping in a magnetic topological material. By performing high-resolution angle-resolved photoemission measurements on ${\mathrm{EuCd}}_2{\mathrm{As}}_2$, we found that a huge amount of hole doping can be introduced into the sample surface due to surface absorption. The electronic structure exhibits a dramatic change with the hole doping which cannot be described by a rigid band shift. Prominent band splitting is observed at high doping which corresponds to a doping-induced magnetic transition at low temperature (below $\sim 15$ K) from an antiferromagnetic state to a ferromagnetic state. These results have established a detailed electronic phase diagram of ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ where the electronic structure and the magnetic structure change systematically and dramatically with the doping level. They further suggest that the transport, magnetic, and topological properties of ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ can be greatly modified by doping. This work will stimulate further investigations to explore for new phenomena and properties in doping this magnetic topological material.

An investigation of the possibility of optical refrigeration (OR) on zinc-blende cadmium selenide/cadmium sulfide (CdSe/CdS) core/shell structure quantum dots (QDs) has been carried out. Quality samples were synthesized in our laboratory, and significant energy up-conversion photoluminescence (UCPL) was observed in these samples, showing the potential of generating net cooling effects. To better understand and predict the UCPL characteristics of the QDs, a semiempirical model has been developed, showing good agreement with our experimental results. The model takes into account the corresponding quantum yield and cooling efficiency, predicting the possibility of realizing optical refrigeration on a CdSe QD system.

Epsilon-near-zero (ENZ) materials have been demonstrated to exhibit unique electromagnetic properties. Here we propose the concept of a radiative energy band gap for an ENZ nanoparticle coupled with a quantum emitter (QE). The radiative emission of the coupled QE–nanoparticle can be significantly suppressed around the ENZ frequency and substantially enhanced otherwise, yielding an effective energy band gap for radiation. This suppression is effectively invariant with respect to particle size and is therefore an intrinsic property of the ENZ material. Our concept also heralds an alternative pathway to quench the emission from a QE, which may find potential application in quantum information storage.

In this paper we show that conventional current-voltage spectroscopy can provide quantitative information on the dispersion relation of the low-energy electrons of monoelemental group-IV two-dimensional (2D) Dirac materials provided that (1) the 2D material is placed on a substrate with a band gap and (2) the density of states of the scanning tunneling microscopy tip is constant. We have derived an expression for the differential conductivity of a monoelemental group-IV 2D Dirac material that is placed on a substrate with a band gap. The differential conductivity scales as $|E-E_D|e^{b|E-E_D|},$ rather than the commonly assumed $|E-E_D|$ scaling, where $E$ and $E_D$ refer to the energy of the electrons and the Dirac point, respectively. The parameter $b$ is inversely proportional to the Fermi velocity.

We simulated the radiative response of the cavity quantum electrodynamics (QED) coupled to the double quantum dot Cooper pair splitter and analyzed its spectral dependence to get insight into dynamics of the Cooper pair transfers. The model is confined to the energy subspace where two entangled electrons are transferred to two normal electrodes through the interdot singlet state on two proximitized quantum dots. Our research is focused on the Andreev scatterings in the subgap regime, for which the local charge susceptibility $\mathrm{\Pi }\left({\omega }_p\right)$ is derived, by means of Keldysh Green functions, in a whole bias voltage range. In particular, in the large voltage limit, the spectrum of $\mathrm{\Pi }\left({\omega }_p\right)$ is expressed by a simple analytical formula, which shows various dissipation processes related with photon-induced transitions between the Andreev bound states.

The one-dimensional (1D) Kitaev model in the topological phase, with open boundary conditions, hosts Majorana zero modes. These are fermion parity-odd operators that almost commute with the Hamiltonian and manifest in long coherence times for edge degrees of freedom. We obtain higher-dimensional counterparts of such Majorana operators by explicitly computing their closed form expressions in models describing 2D and 3D higher-order superconductors. Due to the existence of such Majorana zero modes, the coherence time of the infinite temperature autocorrelation function of the corner Majorana operators in these models diverges with the linear system size. In the presence of a certain class of orbital-selective dissipative dynamics, the coherence times of half of the corner Majorana operators are enhanced, while the time correlations corresponding to the remaining corner Majoranas decay much faster as compared with the unitary case. We numerically demonstrate robustness of the coherence times to the presence of disorder.

ABC trilayer graphene aligned with hexagonal boron nitride (ABC/hBN) and other moiré systems have shown insulating phases at integer fillings of the moiré lattice. The role of Mott physics in these insulating states has been questioned by observations of correlated states in a nonaligned ABC trilayer, but recent photocurrent experiments in aligned samples are consistent with the existence of a Mott insulating state at half filling. Using dynamical mean-field theory we address the effect of Mott correlations in ABC/hBN. We show that, at experimentally relevant interaction values, the electronic states are strongly affected by a significant spectral weight transfer not present without alignment to hBN. This effect, which emerges at interactions considerably smaller than $U_{\mathrm{Mott}}$ (at which the Mott metal-insulator transition takes place) and does not require symmetry breaking, also impacts the electronic properties at temperatures above the ordering transitions producing anomalous temperature and doping dependencies. Close to the Mott transition, the intramoiré unit cell interactions promote an antiferromagnetic state, probably breaking the $C_3$ symmetry, that would compete with the ferromagnetic exchange interactions to determine the ground state.

We predict the instability of the quantum spin-1 chain material with respect to the spin nematic ordering. For the spin subsystem the spin nematic order parameter is related to the onset of single-ion spin anisotropy. The ordering is caused by the coupling to the elastic subsystem of the crystal or, for spin-1 ultracold bosons in a one-dimensional optical lattice, by the interaction with a Bose-Einstein condensate. Our conclusions are based on the exact integrability of the spin model and on numerical simulations for the nonintegrable cases. Our exact results also describe the behavior of interacting gluons within the lattice toy Yang-Mills-like model, in which spontaneous and field-induced symmetry breaking can be realized.

We investigate the microwave spin excitations of the cubic chiral magnet ${\mathrm{Fe}}_{0.75}{\mathrm{Co}}_{0.25}\mathrm{Si}$ as driven by the thermal modulation of magnetic interactions via laser heating and probed by time-resolved measurements of the magneto-optical Kerr effect. Focusing on the topologically nontrivial skyrmion lattice state, the dynamic properties in thermodynamic equilibrium are compared with those of a metastable state prepared by means of rapid field cooling. In both cases, we find precessional and exponential contributions to the dynamic response, characteristic of a breathing mode and energy dissipation, respectively. When taking into account the universal scaling as a function of temperature, the precession frequencies in the equilibrium and metastable skyrmion state are in excellent quantitative agreement. This finding highlights that skyrmion states far from thermal equilibrium promise great flexibility, for instance, with respect to temperature and field scales, both for possible microwave applications and for the study of fundamental properties.

Multicomponent spin-singlet superconductors with competing 0- and $\pi$-pairing couplings, as in $s_{++}$ and $s_{\pm }$ phases, are close to instabilities with a spontaneous breaking of time-reversal symmetry. We demonstrate that the modification of the kinetic energy of superconducting electrons in a doubly connected superconducting cylinder, determined by the applied flux, generally drives transitions from chiral superconducting states to configurations that are time-reversal symmetric. This magneto-topological-induced changeover is investigated by means of a Ginzburg-Landau approach for a two-band superconductor with interband interactions and impurity scattering investigated for the case of a sample in the form of a mesoscopically thin-walled cylinder. We find that the application of a magnetic flux can convert a chiral $s_{\pm }+i{s}_{++}$ state into a $s_{\pm }$ configuration and vice versa or tune the energy splitting of chiral states having inequivalent pairing amplitudes. We discuss signatures for the detection of these phases and of the corresponding transitions in mesoscopic superconducting loops.

Resonant inelastic x-ray scattering (RIXS) studies across the Ce $M_5$ edge have been carried out to investigate the electronic structure of the ferromagnetic ${\mathrm{CeAgSb}}_2$ Kondo system. The RIXS spectra exhibit energy loss features corresponding to final states usually observed by combining photoemission and inverse photoemission spectroscopy. At low energy loss, a clear signature of the spectral features corresponding to the spin-orbit interaction is also observed. Polarization dependence provides evidence for the ${}^1{S}_0$ symmetry singlet ground state by a total suppression of the $f^0$ final state. A simplified single-impurity Anderson model combined with full multiplet theory allows an accurate description of the spin-charge excitations. The RIXS data also reveal a strong temperature $T$ dependence of the fluorescencelike structure. We conjecture that this behavior reflects the $T$ dependence of the Kondo resonance.