The superposition of atomic vibrations and flexoelectronic effect gives rise to a cross correlation between free charge carriers and temporal magnetic moment of phonons in conducting heterostructures under an applied strain gradient. The resulting dynamical coupling is expected to give rise to quasiparticle excitations called magnetoelectronic electromagnons that carry electronic charge and temporal magnetic moment. Here, we report experimental evidence of magnetoelectronic electromagnons in the freestanding degenerately doped $p$-Si based heterostructure thin film samples. These quasiparticle excitations give rise to long-distance ($>100 \mu \mathrm{m}$) spin transport, demonstrated using spatially modulated transverse magnetothermoelectric and nonlocal resistance measurements. The magnetoelectronic electromagnons are nonreciprocal and give rise to large magnetochiral anisotropy $\left(0.352{\mathrm{A}}^{-1}{\mathrm{T}}^{-1}\right)$ that diminishes at lower temperatures. The superposition of nonreciprocal magnetoelectronic electromagnons gives rise to longitudinal and transverse modulations in charge carrier density, spin density, and magnetic moment, demonstrated using the Hall effect and edge dependent magnetoresistance measurements, which can also be called inhomogeneous magnetoelectronic multiferroic effect. These quasiparticle excitations are analogous to photons where time dependent polarization and temporal magnetic moment replace electric and magnetic field, respectively, and most likely topological because they manifest topological Nernst effect. Hence, the magnetoelectronic electromagnon can potentially give rise to quantum interference and entanglement effects in conducting solid state systems at room temperature in addition to efficient spin transport.

Modulation of the Dirac cone of graphene has been highly desired to enrich the exotic properties of graphene. Intercalation of Li into multilayer graphene could lead to the gap opening of the Dirac cone of graphene. Here, using density functional theory calculations, we identify the stable intercalated structure and the corresponding evolution of band structures in the intercalation process of Li into bilayer graphene (BLG). The generalized Kekulé order beyond the traditional $\sqrt{3}\times \sqrt{3}$ supercell has been observed to modulate the Dirac cones of BLG by opening a gap or splitting the electron and hole pocket, contributed by the Kekulé-O and the Kekulé-Y distortion, respectively. Our work provides a further understanding of the modulation of the Dirac cone of graphene and can serve as a landmark for experiment to investigate the Li-intercalated BLG.

We report the existence of a low-temperature polar phase in $\mathrm{PbZr}{\mathrm{O}}_3$ below 270 K. The temperature dependence of resultant polarization was assigned from pyroelectric current changes measured after poling the single crystal or ceramic in a DC electric field. This was observed in single crystals and ceramics and may have a connection with the presence of polar (ferrielectric) antiphase boundaries inside the antiferroelectric phase. The transition point is demonstrated by changes in domain structure and anomalies in dielectric permittivity and losses in as-grown single crystals and ceramic samples.

Proximity-induced superconductivity in fractional quantum Hall edges is a prerequisite to proposed realizations of parafermion zero modes. A recent experimental work [Gül et al., Phys. Rev. X 12, 021057 (2022)] provided evidence for such coupling, in the form of a crossed Andreev reflection signal, in which electrons enter a superconductor from one chiral mode and are reflected as holes to another, counterpropagating chiral mode. Remarkably, while the probability for crossed Andreev reflection was small, it was stronger for $\nu =1/3$ fractional quantum Hall edges than for integer ones. We theoretically explain these findings, including the relative strengths of the signals in the two cases and their qualitatively different temperature dependencies. An essential part of our model is the coupling of the edge modes to normal states in the cores of Abrikosov vortices induced by the magnetic field, which provide a fermionic bath. We find that the stronger crossed Andreev reflection in the fractional case originates from the suppression of electronic tunneling between the fermionic bath and the fractional quantum Hall edges. Our theory shows that the mere observation of crossed Andreev reflection signal does not necessarily imply the presence of localized parafermion zero modes, and suggests ways to identify their presence from the behavior of this signal in the low-temperature regime.

The one-dimensional Kitaev chain, being one of the most significant superconductor models that support Majorana fermions, has been considered as a highly probable method to host nonlocal qubits for topological quantum computation. Here we theoretically introduce the concept into the classical-wave systems and report the first experimental prototype of the acoustic Kitaev chain. We rigorously demonstrate the acoustic correspondence of the Kitaev chain and experimentally observe the classical unpaired Majorana-like zero mode in a well-designed acoustic spinless $p$-wave superconductor. In particular, clear physical evidence also demonstrates such exotic acoustic modes can be manipulated to a certain extend like a quasiparticle, which is directly identified by employing a Kitaev “keyboard.” These results are expected to open new avenues for novel applications of topological acoustics.

Spatial dependence of magnetization dynamics in a ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ film exposed to a magnetic-field gradient has been investigated by measuring local spin pumping and inverse spin-Hall effects. The result shows that, when microwaves are irradiated locally, magnetization precession is excited at a far distant position from the microwave irradiation position. By measuring the field and microwave frequency dependence, we found that the observed magnetization dynamics is attributed to nonlocal resonance of magnetization as well as the spatial change in the spin-wave dispersion under the magnetic-field gradient, which can be applied to realizing an innate microwave spectrometer: a spin-wave cochlea.

The frustrated triangular Ising magnet ${\mathrm{Ca}}_3{\mathrm{Co}}_2{\mathrm{O}}_6$ has long been known for an intriguing combination of extremely slow spin dynamics and peculiar magnetic orders, such as the evenly spaced nonequilibrium metamagnetic magnetization steps and the long-wavelength spin density wave (SDW) order, the latter of which is essentially an emergent crystal of solitons. Recently, an elaborate field-cooling protocol to bypass the low-field SDW phase was proposed to overcome the extraordinarily long timescale of spin relaxation that impeded previous experimental studies in equilibrium, which may point to a deep connection between the low-temperature slow relaxation and the cooling process passing through the low-field SDW phase. As the first step to elucidate the conjectured connection, we investigate the magnetic field induced deformation of the SDW state and incommensurate-commensurate transitions, thereby mapping out the equilibrium in-field phase diagram for a realistic three-dimensional lattice spin model by using Monte Carlo simulations. We also discuss Ginzburg-Landau theory that includes several umklapp terms as well as an effective sine-Gordon model, which can qualitatively explain the observed magnetic field induced deformation of the SDW microphases.

We present an ab initio method for electronic structure calculations, which accounts for the interaction of electrons and magnons in ferromagnets. While it is based on a many-body perturbation theory we approximate numerically complex quantities with quantities from time-dependent density functional theory. This results in a simple and affordable algorithm which allows us to consider more complex materials than those usually studied in this context ($3d$ ferromagnets) while still being able to account for the nonlocality of the self-energy. Furthermore, our approach allows for a relatively simple way to incorporate self-consistency. Our results are in a good agreement with experimental and theoretical findings for iron and nickel. Especially the experimental exchange splitting of nickel is predicted accurately within our theory. Additionally, we study the half-metallic ferromagnet NiMnSb concerning its nonquasiparticle states appearing in the band gap due to spin-flip excitations.

The theory of localized spin-wave excitations in random-anisotropy magnets has been developed. Starting with a pure Heisenberg ferromagnet, we study the evolution of standing spin waves in a finite-size sample towards localized modes on increasing the strength of random anisotropy. Profiles of the localized modes and their phases are analyzed and visualized in a two-dimensional sample. Localization length is obtained by several methods and its dependence on random anisotropy is computed. The connection between the localization of spin excitations and the broadband nature of the absorption of microwave power by random-anisotropy magnets is elucidated.

The sulfur-substituted FeSe, ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$, is one of the unique systems that provides an independent tunability of nematicity, antiferromagnetism, and superconductivity under pressure ($p$). Recently, Rana et al. [K. Rana et al., Phys. Rev. B 101, 180503(R) (2020)] reported, from ${}^{77}\mathrm{Se}$ nuclear magnetic resonance (NMR) measurements on ${\mathrm{FeSe}}_{0.91}{\mathrm{S}}_{0.09}$ under pressure, that there exists a clear role of nematicity in the relationship between antiferromagnetic (AFM) spin fluctuations and the superconducting transition temperature ($T_{\mathrm{c}}$), where the AFM spin fluctuations are more effective in enhancing $T_{\mathrm{c}}$ in the absence of nematicity than with nematicity. Motivated by the work, we carried out ${}^{77}\mathrm{Se}$ NMR measurements on ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ with $x$ = 0.15 and 0.29 under pressure up to 2.10 GPa to investigate the relationship in a wide range of $x$ in the ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ system. Based on the new results together with the previously reported data for $x=0$ [P. Wiecki et al., Phys. Rev. B 96, 180502(R) (2017)] and 0.09 [K. Rana et al. Phys. Rev. B 101, 180503(R) (2020)], we established a $p-x$–temperature ($T$) phase diagram exhibiting the evolution of AFM spin fluctuations. From the systematic analysis of the NMR data, we found that the superconducting (SC) state in a nematic state arises from a non-Fermi-liquid state with strong stripe-type AFM spin fluctuations, while the SC state without nematicity comes from a Fermi-liquid state with mild stripe-type AFM spin fluctuations. Furthermore, we show that the previously reported impact of nematicity on the relationship between AFM fluctuations and superconductivity holds throughout the wide range of $x$ from $x=0$ to 0.29 in ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ under pressure. We discuss the origin of the role of nematicity in terms of the different numbers of hotspots on Fermi surfaces with and without nematicity.

Quasicrystals are long-range ordered, yet not periodic, and thereby present a fascinating challenge for condensed matter physics, as one cannot resort to the usual toolbox based on Bloch's theorem. Here, we present a numerical method for constructing the Hubbard Hamiltonian of nonperiodic potentials without making use of Bloch's theorem and apply it to the case of an eightfold rotationally symmetric two-dimensional optical quasicrystal that was recently realized using cold atoms. We construct maximally localized Wannier functions and use them to extract onsite energies, tunneling amplitudes, and interaction energies. In addition, we introduce a configuration-space representation, where sites are ordered in terms of shape and local environment, that leads to a compact description of the infinite-size quasicrystal in which all Hamiltonian parameters can be expressed as smooth functions. The configuration-space picture serves as an aperiodic analog of the Brillouin zone, and allows one to efficiently describe the quasicrystal in the thermodynamic limit, enabling new analytic arguments on the topological structure and many-body physics of these models. For instance, we use it to conclude that this quasicrystal will host unit-filling Mott insulators in the thermodynamic limit.

The radiation pressurelike coupling between magnons and phonons in magnets can modify the phonon frequency (magnomechanical spring effect) and decay rate (magnomechanical decay) via dynamical backaction. Such effects have been recently observed by coupling the uniform magnon mode of a magnetic sphere (the Kittel mode) to a microwave cavity. In particular, the ability to evade backaction effects was demonstrated [C. A. Potts et al., Phys. Rev. B 107, L140405 (2023)], a requisite for applications such as magnomechanical-based thermometry. However, deviations were observed from the predicted magnomechanical decay rate within the standard theoretical model. In this work, we account for these deviations by considering corrections due to (i) magnetic Kerr nonlinearities and (ii) the coupling of phonons to additional magnon modes. Provided that such additional modes couple weakly to the driven cavity, our model yields a correction proportional to the average Kittel magnon mode occupation. We focus our results on magnetic spheres, where we show that the magnetostatic Walker modes couple to the relevant mechanical modes as efficiently as the Kittel mode. Our model yields excellent agreement with the experimental data.

Here, we report the possibility to excite ultrashort spin waves in ferromagnetic thin films by using time-harmonic electromagnetic fields with terahertz frequency. Such ultrafast excitation requires to include inertial effects in the description of magnetization dynamics. In this respect, we consider the inertial Landau-Lifshitz-Gilbert equation and develop analytical theory for exchange-dominated inertial spin waves. The theory predicts a finite limit for inertial spin-wave propagation velocity, as well as spin-wave spatial decay and lifetime as functions of material parameters. Then, guided by the theory, we perform numerical micromagnetic simulations that demonstrate the excitation of ultrashort inertial spin waves (20-nm long) propagating at finite speed in a confined magnetic nanodot. The results are in agreement with the theory and provide the order of magnitude of quantities observable in realistic ultrafast dynamics experiments.

Recently, a helicity-dependent photocurrent was reported in Bi single-layer thin films. It is proposed that the origin of this photocurrent is the combination of photon-spin conversion and spin-charge conversion effects in Bi, and efficient spin conversion in Bi is expected. In this study, we measure two types of terahertz (THz) emissions from Bi/Co bilayer films induced by spin current generation using laser induced demagnetization of the Co layer and the photon-spin conversion effect in the Bi layer to investigate the spin current induced by the two mechanisms simultaneously. We clearly observe different Bi thickness dependences of peak intensity and bandwidth for THz spin current in two experiments, i.e., spin current induced by demagnetization of Co and by photon-spin conversion in Bi. The different Bi thickness dependences of spin current intensity and bandwidth in two experiments are caused by different spin relaxation properties of optically excited spin currents in Bi layers.

Giant magnetoresistance (GMR) in bulk nonmagnetic compounds has received considerable attention since this phenomenon challenged the classical understanding of electron transport under a magnetic field. Here, we report magnetotransport properties of the diamagnetic intermetallic compound ${\mathrm{YCd}}_6$ for applied magnetic fields up to 35 T and temperatures down to 0.4 K that reveal GMR. We argue that the large MR value can be explained in terms of field-induced pseudogaps on a Fermi surface. These results are relevant to the understanding of the Fermi-surface topology of quasicrystal approximants.

To date, none of the ab initio molecular dynamics simulations of polystyrene, often used as an ablator material in inertial confinement fusion targets, with the standard ground-state exchange-correlation (XC) functional in density-functional theory can satisfactorily agree with experiments in terms of reflectivity measurements. We use recently developed thermal strongly constrained and appropriately normed Laplacian-dependent metageneralized gradient approximation XC density functional (T-SCAN-L) and thermal hybrid XC density functional (KDT0) to show that the inclusion of thermal and inhomogeneity effects is crucial for accurate prediction of structural evolution and corresponding insulator-metal transition (IMT) during shock compression. Optical reflectivity calculated as an indicator of IMT is in perfect accord with experimental data.

We study the dynamics of a class of integrable non-Hermitian free-fermionic models driven periodically using a continuous drive protocol characterized by an amplitude $g_1$ and frequency ${\omega }_D$. We derive an analytic, albeit perturbative, Floquet Hamiltonian for describing such systems using Floquet perturbation theory with $g_1^{-1}$ being the perturbation parameter. Our analysis indicates the existence of special drive frequencies at which an approximately conserved quantity emerges. The presence of such an almost conserved quantity is reflected in the dynamics of the fidelity, the correlation functions, and the half-chain entanglement entropy of the driven system. In addition, it also controls the nature of the steady state of the system. We show that one-dimensional transverse field Ising model, with an imaginary component of the transverse field, serves as an experimentally relevant example of this phenomenon. In this case, the transverse magnetization is approximately conserved; this conservation leads to complete suppression of oscillatory features in the transient dynamics of fidelity, magnetization, and entanglement of the driven chain at special drive frequencies. We discuss the nature of the steady state of the Ising chain near and away from these special frequencies, demonstrate the protocol independence of this phenomenon by showing its existence for discrete drive protocols, and suggest experiments which can test our theory.