In this paper we consider the dynamics of a chain of many coupled kicked rotors with dissipation. We map a rich phase diagram with many dynamical regimes. We focus mainly on a regime where the system shows period doubling, and forms patterns that are persistent and depend on the stroboscopic time with period double than that of the driving: The system shows a form of spatiotemporal ordering analogous to quantum Floquet time crystals. Spatiotemporally ordered patterns can be understood by means of a linear-stability analysis that predicts an instability region that contains the spatiotemporally ordered regime. The boundary of the instability region coincides with the lower boundary of the spatiotemporally ordered regime, and the most unstable mode has length scale double than the lattice spacing, a feature that we observe in the spatiotemporally ordered patterns: Period doubling occurs both in time and space. We propose an implementation of this model in an array of SQUID Josephson junctions with a pulsed time-periodic flux.

Materials hosting intrinsic room-temperature ferromagnetism have significant application in spintronics. In this context, the transition metal sulfide chromium telluride (${\mathrm{Cr}}_x{\mathrm{Te}}_y$) has sparked significant attention due to its room-temperature ferromagnetism, as well as high magnetic anisotropy, easy tunability, and air stability. This study carefully examines the magnetic characteristics of an intrinsic room-temperature ferromagnetic ${\mathrm{Cr}}_3{\mathrm{Te}}_4$ single crystal. Magnetization measurements identify a paramagnetic-to-ferromagnetic (PM-FM) phase transition at $T_C\sim 322$ K and high magnetic anisotropy. Meanwhile, a coexistence of ferromagnetism and antiferromagnetism is unveiled below $T_N\sim 90$ K. A systematic investigation of magnetization isotherms collected near $T_C$ provides the asymptotic critical exponents $\beta =0.365\left(5\right), \gamma =1.212\left(9\right), \delta =4.580\left(4\right)$ for $H//ab$, and $\beta =0.370\left(3\right), \gamma =1.329\left(1\right), \delta =4.554\left(9\right)$ for $H//c$. The obtained critical exponents for $H//ab$ and $H//c$ suggest strong anisotropic and multiple magnetic interactions in ${\mathrm{Cr}}_3{\mathrm{Te}}_4$. The comprehensive $H-T$ phase diagrams for $H//ab$ and $H//c$ are constructed using universal scaling and detailed magnetization, revealing strong field-dependent anisotropic room-temperature ferromagnetism and coexistence of ferromagnetism, antiferromagnetism, and noncollinear ferromagnetism. The multiple phases demonstrate that the magnetic couplings in ${\mathrm{Cr}}_3{\mathrm{Te}}_4$ are mediated by intralayer super exchange, interlayer double exchange, and direct exchange.

We extend the Mattis-Bardeen theory for the dynamical response of superconductors to include different types of Hall responses. This is possible thanks to a recent modification of the quasiclassical Usadel equation, which allows for analyzing Hall effects in disordered superconductors and including the precise frequency dependence of such effects. Our results form a basis for analyzing dynamical experiments especially on novel thin-film superconductors, where ordinary Hall and spin Hall effects can both show up.

We investigate the interplay between altermagnetic spin-splitting and nonsymmorphic symmetries using the space group No. 62 as a testbed. Studying different magnetic orders by means of first-principles calculations, we find that the altermagnetism (AM) is present in the $C$-type magnetic configuration while it is absent for the $G$-type and $A$-type configurations due to different magnetic space group types. The nonsymmorphic symmetries constrain the system to a fourfold degeneracy at the border of the Brillouin zone with semi-Dirac dispersion. In the case of large hybridization as for transition metal pnictides, the interplay between AM and nonsymmorphic symmetries generates an intricate network of several crossings and anticrossings that we describe in terms of semi-Dirac points and glide symmetries. When we add the spin-orbit coupling (SOC), we find a Néel-vector dependent spin-orbit splitting at the time-reversal invariant momenta points since the magnetic space groups depend on the Néel vector. The magnetic space group type I produces antiferromagnetic hourglass electrons that disappear in the type III. When the Néel vector is along $x$, we observe a glide-protected crossing that could generate a nodal line in the altermagnetic phase. The SOC splits the remaining band crossings and band anticrossings, producing a large anomalous Hall effect in all directions excluding the Néel-vector direction.

The Kähler-Dirac fermion, recognized as an elegant geometric approach, offers an alternative to traditional representations of relativistic fermions. Recent studies have demonstrated that symmetric mass generation (SMG) can precisely occur with two copies of Kähler-Dirac fermions across any space-time dimensions. This conclusion stems from the study of anomaly cancellation within the fermion system. Our research provides an alternative understanding of this phenomenon from a condensed matter perspective, by associating the interacting Kähler-Dirac fermion with the boundary of bosonic symmetry-protected topological (SPT) phases. We show that the low-energy bosonic fluctuations in a single copy of the Kähler-Dirac fermion can be mapped to the boundary modes of a ${\mathbb{Z}}_2$-classified bosonic SPT state, protected by an inversion symmetry universally across all dimensions. This implies that two copies of Kähler-Dirac fermions can always undergo SMG through interactions mediated by these bosonic modes. This picture aids in systematically designing SMG interactions for Kähler-Dirac fermions in any dimension. We present the exact lattice Hamiltonian of these interactions and validate their efficacy in driving SMG.

A highly ordered, Pb-dense $14\times \sqrt{3}$-Pb overlayer was grown on Si(111) using the two-step procedure with formation of the $\sqrt{7}\times \sqrt{3}\text{−}\mathrm{Pb}$ surface [displaying the $1\times 1$ structure at room temperature (RT)] at the first step and RT deposition of additional Pb at the second step until formation of the $14\times \sqrt{3}\text{−}\mathrm{Pb}$ phase with 1.286 monolayers of Pb is completed. The single-domain orientation of the $14\times \sqrt{3}\text{−}\mathrm{Pb}$ layer persists along the entire surface of the terraces which are typically as wide as dozens of nanometers and in the selected areas might exceed a hundred nanometers. The $14\times \sqrt{3}\text{−}\mathrm{Pb}$ phase hosts the superconductivity with the critical temperature $T_c=2.08$ K which exceeds all ever reported values for the single-atom Pb layers on Si(111).

Unconventional topological quasiparticles have recently garnered significant attention in the realm of condensed matter physics. Here, based on first-principles calculations and symmetry analysis, we reveal the coexistence of multiple types of interesting unconventional topological quasiparticles in the phonon spectrum of the chiral crystal ${\mathrm{CsBe}}_2{\mathrm{F}}_5$. Specifically, we identified eight entangled phonon bands in ${\mathrm{CsBe}}_2{\mathrm{F}}_5$, which give rise to various unconventional topological quasiparticles, including the spin-1 Weyl point, the charge-2 Dirac point, the nodal surface, and the hourglass nodal loop. We demonstrate that these unconventional topological quasiparticles are protected by crystal symmetry. We show that there are two large Fermi arcs connecting projections of the bulk spin-1 Weyl point and charge-2 Dirac point on the (001) surface and across the entire surface Brillouin zone. Our work not only elucidates the intriguing topological properties of chiral crystals but also provides an excellent material platform for exploring the fascinating physics associated with multiple types of unconventional topological quasiparticles.

We report on the growth of one-dimensional (1D) chains of the prochiral quinacridone (QA) molecule on ultrathin KCl films on Cu(111) in ultrahigh vacuum. Using low-temperature scanning tunneling microscopy (STM), we observe straight homochiral 1D chains of QA molecules on one (1L), two (2L), and three (3L) atomic layer thick (100)-terminated KCl islands. The KCl films mostly consist of 2L-thick KCl islands delineated by long polar and short nonpolar edges. These 2L-thick KCl islands are topped by smaller one-atom-thick KCl islands or pits, which are delineated by nonpolar step edges. We find that QA chains can nucleate at these nonpolar step edges or on top of KCl terraces without assistance of step edges. In both cases, the longest straight QA chains observed grow along the KCl $\langle 100\rangle$ directions or slightly rotated (typically less than ${10}^{\circ }$) from them. Intermolecular distances ranging from 6.4 Å to 6.8 Å are measured for QA chains on KCl/Cu(111), which is compatible with hydrogen bonds between neighboring flat-lying QA molecules. These intermolecular distances being larger than the measured KCl lattice parameter (i.e., 6.21 Å at 78 K), QA chain growth on KCl/Cu(111) is incommensurate. Molecular arrangement models for the QA chains on KCl are proposed, based on the analysis of the STM images.

The topological magnetoelectric effect (TME) is a characteristic property of topological insulators. In this paper, we use a simplified coupled-Dirac-cone electronic structure model to theoretically evaluate the THz and far infrared Kerr and Faraday responses of thin films of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ with up to $N=10$ septuple layers with the goal of clarifying the relationship between these convenient magnetooptical observables and the TME. We find that for even $N$, the linear Kerr and Faraday responses to an electric field vanish in the low-frequency limit, even though the magnetoelectric response is large and approximately quantized.

Graphene, a material with exceptional physicochemical properties, has been synthesized on a variety of substrates. However, prior theoretical studies have suggested that carbon (C) clusters are typically less stable thermodynamically compared to individual C monomers on most transition metal substrates. Taking the Pt(111) surface as a case study, we introduce a unified mechanism termed the “self-surfactant effect” that promotes the efficient growth of graphene on Pt(111). This mechanism incorporates two key processes: edge passivation and repulsion minimization. The self-surfactant effect serves as an essential bridge between theoretical predictions and experimental observations, enhancing the growth of graphene in two ways: (1) by strengthening the interaction between C clusters and the substrate through edge passivation, and (2) by minimizing repulsion between the inner atoms of C clusters and the substrate. Intriguingly, our results reveal a linear correlation between the formation energies of C clusters on the Pt(111) surface and the ratio of peripheral atoms to the total number of atoms within the clusters. These insights not only advance our understanding of graphene growth but may also have broader implications for other heteroepitaxial systems.

Inelastic neutron scattering provides a powerful probe of the magnetic excitations of quantum magnets. Altermagnets have recently emerged as a new class of magnets with vanishing net magnetization characteristic of antiferromagnets and with a spin-split electronic structure typical of ferromagnets. Here we introduce a minimal Hubbard model with two-sublattice orthorhombic anisotropy as a framework to study altermagnetism. Using unrestricted Hartree-Fock calculations, we find an altermagnetic state for this model that evolves from a metallic state to an insulating state with increasing Hubbard-$U$ Coulomb repulsion. We then examine the inelastic neutron scattering response in these states using random-phase approximation calculations of the dynamic spin susceptibility ${\chi }^{″}(\mathbf{q},\omega )$. We find that the magnetic excitation spectrum depends on its chirality for $\mathbf{q}$ along certain directions in reciprocal space, an observation that may be used in inelastic neutron scattering experiments as a probe of altermagnetism.

The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction, which is responsible for the formation of topologically protected spin textures in chiral magnets. Here, by measuring the dispersion relation of the DM energy, we quantify the atomistic DMI in a model system, i.e., a Co double layer on Ir(001). We unambiguously demonstrate the presence of a chirality-inverted DMI, i.e., a sign change in the chirality index of DMI from negative to positive, when comparing the interaction between nearest neighbors to that between neighbors located at longer distances. The effect is in analogy to the change in the character of the Heisenberg exchange interaction from, e.g., ferromagnetic to antiferromagnetic. We show that the pattern of the atomistic DMI in epitaxial magnetic structures can be very complex and provide critical insights into the nature of DMI. We anticipate that the observed effect is general and occurs in many magnetic nanostructures grown on heavy-element metallic substrates.

We theoretically investigate the effects of surface acoustic waves (SAWs) on an electric-field-driven sliding motion of a one-dimensional charge density wave (CDW), which is initially pinned by impurities. By numerically analyzing an extended Fukuyama-Lee-Rice model, we show that a mechanical vibration of the SAW, which, in the model, is assumed to affect the CDW via the pinning site in the form of temporally oscillating pinning parameters, induces Shapiro steps with self-similarity, i.e., the devil's staircase, in the current-voltage characteristics. It is also found that when the SAW acts as the vibration in the pinning strength, the mechanism of the mode locking (harmonic and subharmonic responses) leading to the occurrence of the Shapiro steps is modified, and as a result, the fractal dimension and parameter dependence of the SAW-induced staircase can be considerably different from those for the conventional ac-electric-field-induced one. This suggests that an unconventional type of fractal phenomena can emerge in the SAW-induced CDW dynamics.

Out-of-time-ordered correlators (OTOCs) are useful tools for investigating foundational questions such as thermalization in closed quantum systems because they can potentially distinguish between integrable and nonintegrable dynamics. Here, we discuss the properties of wavefronts of OTOCs by focusing on the region around the main wavefront at $x=v_{B}t$, where $v_B$ is the butterfly velocity. Using a Heisenberg spin model as an example, we find that the leading edge of a propagating Gaussian with the argument $-m\left(x\right){(x-v_{B}t)}^2+b\left(x\right)t$ gives an excellent fit to the region around $x=v_{B}t$ for both the free and chaotic cases. However, the scaling in these two regimes is very different: in the free case the coefficients $m\left(x\right)$ and $b\left(x\right)$ have an inverse power law dependence on $x$, whereas in the chaotic case they decay exponentially. We conjecture that this result is universal by using catastrophe theory to show that, on the one hand, the wavefront in the free case has to take the form of an Airy function and its local expansion shows that the power law scaling seen in the numerics holds rigorously and, on the other hand, an exponential scaling of the OTOC wavefront must be a signature of nonintegrable dynamics. We find that the crossover between the two regimes is smooth and characterized by an $\mathsf{S}$-shaped curve giving the lifting of Airy nodes as a function of a chaos parameter. This shows that the Airy form is qualitatively stable against weak chaos and consistent with the concept of a quantum Kolmogorov-Arnold-Moser theory.

We clarify the nature of hafnia as a proper ferroelectric and show that there is a shallow double well involving a single soft polar mode as in well-known classic ferroelectrics. Using symmetry analysis, density functional theory structural optimizations with and without epitaxial strain, and density functional perturbation theory, we examine several important possible hafnia structures derived ultimately from the cubic fluorite structure, including baddeleyite $(P{2}_1/c)$, tetragonal antiferroelectric $P{4}_{2}nmc$, $Pbca$ (nonpolar and brookite), ferroelectric rhombohedral $(R3m–\mathrm{and}–R3)$, $Pmn{2}_1$, and $Pca{2}_1$ structures. The latter is considered to be the most likely ferroelectric phase seen experimentally and has an antiferroelectric parent with space group $Pbcn$, with a single unstable polar mode and a shallow double well with a well depth of 24 meV/atom. Strain is not required for switching or other ferroelectric properties, nor is coupling of the soft mode with any other modes within the ferroelectric $Pca{2}_1$, $Pmn{2}_1$, $R3m$, or $R3$ phases.

The topological surface state arising from the nontrivial topology of the bulk band structure has attracted a wide range of interest. Compared with electrons, the magnon propagation in magnetic materials can be more intuitively reflected in the spin precession and generate different effects. Using molecular dynamics simulations, we study the real-space evolution of the magnon topological surface state in ${\mathrm{Cu}}_3{\mathrm{TeO}}_6$, a three-dimensional antiferromagnet with Dzyaloshinskii-Moriya interaction. We observe a coherent wave-packet propagation on the surface without attenuation into the bulk. As the intensity of the chiral Dzyaloshinskii-Moriya interaction increases, spin-dependent chirality of magnons appears on the surface. Such behavior suggests that ${\mathrm{Cu}}_3{\mathrm{TeO}}_6$ displays the magnon spin Nernst effect, i.e., the system generates a transverse net spin flow after applying a longitudinal temperature gradient. In our numerical calculations, when the intensity of the Dzyaloshinskii-Moriya interaction is about $10\%$ of the nearest neighbor exchange interaction, the spin Nernst coefficient in this material is estimated to be around ${\alpha }_{yz}=1–3\times {10}^{-16}\mathrm{J}/\mathrm{mK}$.

We consider a ferromagnetic particle levitated in air under microwave irradiation and theoretically study the noise in its rigid-body rotation induced by the gyromagnetic effect. This rotational noise includes useful information on angular momentum transfer from the magnetization to the rigid-body rotation, such as the unit of angular momentum per one spin relaxation process. We formulate the rotational noise in terms of the Lindblad equation, which describes the quantum stochastic process, and estimate it in the case of realistic experimental parameters. We show that a bifurcation phenomenon observed in our setup amplifies the noise and, therefore, can be exploited, making an accurate measurement of the rotational noise.

We present a comprehensive study on the nonequilibrium properties of superconducting nanoconstriction junctions in steady-state and time-dependent dynamic regimes. By measuring the current-voltage characteristics of single constriction and micro-superconducting quantum interference devices with nanobridges, we observe a series of distinct voltage-step jumps in the dissipative state, which are associated with the appearance of the excess current. Through detailed analysis, we identify different mechanisms that contribute to the enhancement of superconductivity under varying bias voltages. In the time-dependent dynamic regime where the bias voltage $V$ significantly exceeds the superconducting gap voltage $(V\gg \mathrm{\Delta }/e)$, the nanoconstriction behaves as a single phase-slip center (PSC). The voltage steps observed in this regime signify the phase-slipping dynamics at PSC, which effectively mitigates the self-heating effects. Conversely, in the steady-state regime where $V$ is lower than the gap voltage, the voltage steps arise from multiple Andreev reflections. We demonstrate that the interplay of Andreev quasiparticles and Josephson supercurrent plays a crucial role in restoring the phase coherence of the dissipation currents. Our findings provide an insightful understanding of nonequilibrium quasiparticle relaxation dynamics in superconducting nanometallic weak links and offer practical implications for potential applications.