We report a comprehensive characterization of the magnetic, electrical transport, Raman spectra, and thermal properties of the single-crystalline Zintl-type material ${\mathrm{EuIn}}_2{\mathrm{P}}_2$. The compound crystallizes with a hexagonal unit cell (space group $P{6}_3/mmc$) and orders magnetically at $T_{\mathrm{C}}=24$ K with the Eu magnetic moments aligned ferromagnetically within the $ab$ plane but tilted alternately along the $c$-axis direction. The effective and saturation magnetic moments agree with the theoretical values expected for the ${\mathrm{Eu}}^{2+}$ ion. For a range of several tens of kelvins above $\sim 40$ K, the electrical transport of ${\mathrm{EuIn}}_2{\mathrm{P}}_2$ is dominated by short-range magnetic interactions. The temperature dependence of the electrical resistivity was modeled in terms of variable-range hopping. Another indication of the latter scenario seems to be the observation, for ${\mathrm{EuIn}}_2{\mathrm{P}}_2$, of a quadratic dependence of the negative magnetoresistance on the magnetic field strength and the scaled magnetization. The temperature dependence of the Raman band position and FWHM, as well as the phonon lifetime, confirms the presence of the distinctive regions observed in transport and magnetic studies.

A stable, low-power, and tunable magnon frequency comb (MFC) is crucial for magnon-based precision measurements, quantum information processing, and chip integration. The original method for creating a MFC utilizes the nonlinear interactions between propagating spin waves and localized oscillations of an isolated magnetic texture, e.g., skyrmion. It requires a driving frequency well above the ferromagnetic resonance (FMR) and the spectrum frequency of a MFC will quickly approach the detection limit of a conventional microwave technique after only tens of comb teeth. In addition, the detection and manipulation of a single skyrmion is challenging in experiments due to its high degree of locality. These issues hinder the applications of a MFC. In this work, we report the low-lying MFC with comb frequencies below the FMR in a skyrmion crystal (SkX). We show that the MFC originates from the three-wave mixing between the collective skyrmion gyration and breathing in the SkX. Our findings significantly improve the efficiency of the nonlinear frequency conversion from a single-frequency microwave input and establish a synergistic relationship between the SkX and MFC, which paves the way to coherent information processing and ultrasensitive metrology based on the MFC.

The interplay of different forms of energies in oxide superlattices, such as elastic, electrostatic, and gradient energies, can result in a stable long-range ordered polar vortex structure at room temperature. However, the role between these energies in determining the vortex structure still remains largely elusive due to the intricate interplay. By using a comprehensive in situ TEM apparatus and a prototype system, ${\mathrm{PbTiO}}_3$/${\mathrm{SrTiO}}_3$ superlattice, we demonstrate that the vortex structure undergoes a first-order transition at the temperature around 653 K, while the application of in-plane mechanical stress at such a high temperature results in the reemergence of vortex structure. Cryogenic cooling to 94 K raises the stability of vortices, which would be destabilized by loading of out-of-plane mechanical stress. The results can be reproduced and well interpreted by phase-field simulations. These findings not only reveal the competing role of the temperature and mechanical stress at atomic scale but also demonstrate a feasible way to operate the vortex-based nanodevices working in harsh environments.

Incommensurate heterostructures of two-dimensional (2D) materials, despite their attractive electronic behavior, are challenging to simulate because of the absence of translation symmetry. Experimental investigations of these structures often employ scanning tunneling microscopy (STM); however, there is to date no comprehensive theory to simulate an STM image in such systems. In this paper, we present a geometry-based method to generate STM images in incommensurate van der Waals (vdW) heterostructures, which we call the moiré plane wave expansion model (MPWEM). We generate the STM images using a weighted sum of three image terms: the noninteracting STM images of (1) the substrate layer, (2) the adsorbate layer, and (3) a semi-empirical Fourier expansion of the moiré wave vectors obtained analytically which results from the interaction of (1) and (2). We illustrate and benchmark the model using selected vdW 2D systems composed of structurally and electronically distinct crystals, and show that the method reproduces experimental STM images down to angstrom-scale details. The MPWEM, thanks to its simplicity, can serve as an image generation tool prior to more computationally expensive calculations which are often limited by the number of atoms and the requirement of periodic supercells, and thus offers a promising class of computationally friendly STM simulations, of high relevance in the growing field of twistronics.

This paper investigates the dispersion characteristics of a highly anisotropic metamaterial comprised of metal square patches arranged in a glide-symmetry pattern and submerged in a vacuum. Theoretical formulas are proposed to describe the electromagnetic tensors of a corresponding uniaxial effective medium with dielectric and magnetic responses. In addition, this work employs theoretical analysis and numerical simulations to examine the interaction between the metamaterial and electromagnetic waves across a broad spectral range. Band diagrams and isofrequency contours show good agreement between theoretical and numerical results for low frequencies and certain directions of propagation at higher frequencies. The ease of designing the metamaterial structure for various applications is facilitated by the derived theoretical formulas, which enable accurate prediction of the electromagnetic response across a wide range of frequencies based on geometric parameters.

Anomalous velocity has been derived so far based on the single-band approximation. In this paper, anomalous velocity is derived taking into account multiple energy bands. It is shown that when multiple energy bands are considered, anomalous velocity is actually derived from the velocity term that goes to zero under the single-band approximation. It is also shown that the anomalous velocity based on the single-band approximation is derived improperly from the velocity term that becomes zero in considering multiple energy bands. Furthermore, it is found that unconventional types of anomalous velocity may appear in addition to conventional anomalous velocity. These unconventional anomalous velocities are perpendicular to the electric field and come from the singularity of the magnetic Bloch function in the magnetic Brillouin zone. It is confirmed that conventional and unconventional anomalous velocities can also be derived not only from the steady-state perturbation theory, but also from the time-dependent perturbation theory in which a time-dependent vector potential yielding a uniform electric field is treated as a perturbation.

The Hall effect, ever intriguing since its discovery, has spurred the exploration of its phenomena, intensified by advances in topology and novel materials. Differentiating the ordinary Hall effect from extraordinary properties like the anomalous Hall effect (AHE) is challenging, especially in materials with topological origins. In our study, we leverage semiclassical Boltzmann transport theory and first-principles calculations within the relaxation time approximation to analyze Hall effects comprehensively. We have found that the complex magnetic field dependence of ordinary Hall effect, including the sign reversals, appearing of plateau and nonlinearity, can be understood and reproduced by our approach both for multiband models and realistic topological materials of ZrSiS and ${\mathrm{PtTe}}_2$. The Hall resistivity versus temperature and magnetic fields can be well scaled, similar to Kohler's rule for longitudinal resistivity. This methodology can also accurately model the angular dependent Hall effects such as planar Hall effects of bismuth. These findings indicate that the dependencies of various Hall effects and magnetoresistance on magnetic fields are mainly determined by the details of Fermi surface and the relaxation time. The intrinsic Fermi surface determines the carriers' density, type, and velocity, while the later is mostly influenced by extrinsic factors, such as quality of sample with defects, impurities, and domains. This insight might simplify the understanding of several seemingly complex transport phenomena in nonmagnetic materials, with no need for hypotheses of other sophisticated mechanisms, such as magnetization-induced AHE, Lifshitz transition-induced changes in carrier type, exotic orders like charge density wave, or some delicate scattering of carriers with chiral or nonreciprocal dependence. In order for the completeness of the discussion of Berry curvature, we also discussed the Hall effects when the Berry curvature is considered in the magnetic materials.

A spin-Peierls order emerges in a one-dimensional $S=1$ Heisenberg antiferromagnetic model with single-ion anisotropy, coupled to finite frequency bond phonons, in a magnetic field. Our results indicate that for the pure Heisenberg model, any Peierls transition is suppressed by quantum fluctuations of the phonon field. However, a magnetic field-induced spin-Peierls order is realized in the presence of strong single-ion anisotropy. Contrary to the standard Peierls state, the periodicity of bond strength modulation in this field-induced spin-Peierls state is variable and depends on the strength of the applied field. The nature of the ground state in this new phase and the associated field-driven transitions to and out of this phase are explored using extensive numerical simulations. In particular, we explore the spin and bond correlations and the evolution of bond order modulation with varying magnetic field.

The nonequilibrium Green's function gives access to one-body observables for quantum systems. Of particular interest are quantities such as density, currents, and absorption spectra which are important for interpreting experimental results in quantum transport and spectroscopy. We present an integration scheme for the Green's function's equations of motion, the Kadanoff-Baym equations (KBE), which is both adaptive in the time integrator step size and method order as well as the history integration order. We analyze the importance of solving the KBE self-consistently and show that adapting the order of history integral evaluation is important for obtaining accurate results. To examine the efficiency of our method, we compare runtimes to a state-of-the-art fixed time step integrator for several test systems and show an order of magnitude speedup at similar levels of accuracy.

In this Letter, we demonstrate that the synergetic interplay of topology, nonreciprocity, and nonlinearity is capable of unprecedented effects. We focus on a nonreciprocal variant of the Su-Shrieffer-Heeger chain with local Kerr nonlinearity. We find a continuous family of nonreciprocal edge solitons (NESs) emerging from the topological edge mode, with near-zero energy, in great contrast from their reciprocal counterparts. Analytical results show that this energy decays exponentially towards zero when increasing the lattice size. Consequently, despite the absence of chiral and sublattice symmetries within the system, we obtain zero-energy NESs, which are insensitive to growing Kerr nonlinearity. Even more surprising, these zero-energy NESs also persist in the strong nonlinear limit. Our work may enable different avenues for the control of nonlinear topological waves without requiring the addition of complex chiral- or sublattice-preserving nonlinearities.

We study electron-electron interaction-induced states of twisted bilayer ${\mathrm{MoTe}}_2$ in an out-of-plane magnetic field $B\widehat{\mathbf{z}}$ near one hole per moiré unit cell filling. The three-dimensional phase diagram showing the evolution of competing phases with $B$, interaction strength, and an out-of-plane electric field is presented at electron fillings that follow the Diophantine equation along the Chern number $-\text{sgn}\left(B\right)$ line, that is pointing away from the charge neutral filling, where we find prominent Chern insulators consistent with the experiments. We also explain the experimental absence of prominent Chern insulators along the Chern number $+\text{sgn}\left(B\right)$ line.

The use of hydrodynamic transport theory seems to indicate that the charge diffusion constant $D$ of the one-dimensional (1D) half-filled Hubbard model, whose Drude weight vanishes, diverges for temperature $T>0$, which would imply anomalous superdiffusive charge transport. Here the leading term of that constant is derived for low finite temperatures $k_{B}T/{\mathrm{\Delta }}_{\eta }\ll 1$ where ${\mathrm{\Delta }}_{\eta }$ is the Mott-Hubbard gap. It only diverges in the $T\to 0$ limit, being finite and decreasing upon increasing $T$ within the $k_{B}T/{\mathrm{\Delta }}_{\eta }\ll 1$ regime. Our exact results both provide valuable physical information on a complex quantum problem and bring about the interesting unsolved issue of how charge transport evolves from normal diffusive for $k_{B}T/{\mathrm{\Delta }}_{\eta }\ll 1$ to anomalous superdiffusive in the $k_{B}T\to \infty$ limit.

Strongly interacting electrons in a topologically nontrivial band may form exotic phases of matter. An especially intriguing example of which is the fractional quantum anomalous Hall phase, recently discovered in twisted transition metal dichalcogenides and in moiré graphene multilayers. However, it has been shown to be destabilized in certain filling factors at sub-100 mK temperatures in pentalayer graphene, in favor of a novel integer quantum anomalous Hall phase [Z. Lu, Extended quantum anomalous Hall states in graphene/hBN moiré superlattices, arXiv:2408.10203]. We propose that the culprit stabilizing the fractional phase at higher temperatures is its rich edge state structure. Possessing a multiplicity of chiral modes on its edge, the fractional phase has lower free energy at higher temperatures due to the excess edge mode entropy. We make distinct predictions under this scenario, including the system-size dependency of the fractional phase entropic enhancement, and how the phase boundaries change as a function of temperature.

Using an embedded-atom-method model specifically designed to accurately describe vibrations in alkali metals, we study bulk vibrational structure of Li, Na, K, and Rb when configured in bcc and the close-packed (cp) fcc, hcp, and $9R$ phases. From the vibrational density of states for each phase, we thence find the corresponding vibrational contribution $A_{\mathrm{vib}}\left(T\right)$ to the Helmholtz free energy $A\left(T\right)$. Utilizing (i) differences in $A_{\mathrm{vib}}\left(T\right)$ between the bcc and cp structures and (ii) experimentally inferred thermodynamic transition temperatures for Li and Na (which martensitically transform from bcc to cp phases upon cooling), we extract values for zero-temperature energy differences between the bcc and relevant cp phases. We also put constraints on zero-temperature cp-bcc energy differences for K and Rb, which do not exhibit temperature-induced transitions.

Artificial spin ices provide a controlled platform for investigating diverse physical phenomena, such as geometric frustration, magnetic monopoles, and phase transitions, via deliberate design. Here, we introduce a unique approach by developing artificial spin ice on the surfaces of a three-dimensional cube, which leads to emergent geometric frustration mediated by topologically protected domain walls, distinct from its flat counterparts. These domain walls connect vertices at the cube's corners that act as intrinsic topological defects. Utilizing Monte Carlo simulations, we observe robust, topologically protected correlations among the intrinsic topological defects, regardless of their spatial separation. Our findings demonstrate that three-dimensional surfaces can unveil emergent properties absent in flat architectures.

Ferromagnetic channels subject to spin injection have been theoretically shown to sustain dissipative exchange flows (DEFs). In the strong injection regime, a soliton is stabilized at the injection site, which has been termed a contact soliton DEF or CS-DEF. Here, we investigate the modulation of CS-DEFs as a mechanism to inject magnons into a DEF. By varying the injection current, the parameters connecting the soliton with the DEF via a boundary layer are varied. These lead to a modification in the DEF which is interpreted as a spin piston. The injected magnons follow the expected dispersion relation of DEFs, akin to the Bogoliubov–de Gennes dispersion relation. This work demonstrates that changes in the injected current can pump magnons along a ferromagnetic channel via dissipative exchange flows.

We implement the on-site Coulomb repulsion $U$ and exchange coupling $J$ within the local density approximation (LDA) into the recently developed Dirac-Bogoliubov–de Gennes (DBdG) solver [G. Csire et al., Phys. Rev. B 97, 024514 (2018)] for superconducting heterostructures, by using the screened Korringa-Kohn-Rostoker (SKKR) Green's function method. We apply this implementation to ferromagnetic (FM) Gd layers on a superconducting Nb substrate, where the $U$ and $J$ terms are considered only for the $4f$ orbitals of the Gd layers, and investigate the proximity-induced superconducting properties of the Gd layers by using the implemented $\mathrm{DBdG}+ U$ solver. Our first-principles calculations reveal that with the $U$ and $J$ terms, the density of states at the Fermi level has small contributions from $4f$ orbitals, while without the $U$ and $J$ terms, the contribution of the $4f$ orbitals somewhat increases. For the calculated quasiparticle density of states (DOS), with the $U$ and $J$ terms, there are several secondary satellite gaps, plateau-like regions, and central small V-shaped in-gap states within the bulk superconducting Nb gap, while without the $U$ and $J$ terms, the central V-shaped in-gap states appear within a much wider energy window. The in-gap states are identified to the Yu-Shiba-Rusinov states arising from the individual Gd layers with large magnetic moments rather than due to small magnetization induced in the Nb layers. We find that the normal-state DOS of the FM overlayers at the Fermi level is as important as the magnetic moment of the FM overlayers to the quasiparticle DOS. We also compute the superconducting order parameter as a function of the vertical $z$ coordinate for 10 Gd layers on a Nb substrate. The order parameter abruptly decreases in the proximity to the interface and it oscillates as a function of the $z$ coordinate in the Gd layers. This feature of quasiparticle DOS is qualitatively consistent with the previous studies. The implemented DBdG $+ U$ solver can be used to perform first-principles studies of other strongly correlated superconducting heterostructures as well as bulk superconductors.