We propose a new viewpoint on the study of localization transitions in disordered quantum systems, showing how critical properties can be seen also as a geometric transition in the data space generated by the classically encoded configurations of the disordered quantum system. We showcase our approach to the Anderson model on regular random graphs, known for displaying features of interacting systems, despite being a single-particle problem. We estimate the transition point and verify the critical exponents in agreement with the best-known results in the literature. We provide a simple and coherent explanation of our findings, discussing the applicability of the method in real-world scenarios with a modest number of measurements.

Understanding the dynamics of liquids at the atomic level remains a major challenge. Even though viscosity is one of the most fundamental properties of liquids, its atomistic origin is not fully elucidated. Through inelastic neutron scattering experiment on levitated metallic liquid droplets, the time-dependent pair correlation function, the Van Hove function, was determined for $\mathrm{Z}{\mathrm{r}}_{50}\mathrm{C}{\mathrm{u}}_{50}$ and $\mathrm{Z}{\mathrm{r}}_{80}\mathrm{P}{\mathrm{t}}_{20}$ liquids at various temperatures. The time for change in local atomic connectivity, ${\tau }_{LC}$, which is the timescale of atomic bond cutting and forming, is estimated based on the exponential decay of the nearest neighbor peak of the Van Hove function. At high temperatures above the crossover temperature $T_A, {\tau }_{LC}$ is equal to the Maxwell relaxation time, ${\tau }_M=\eta /G_{\infty }$, where η is the macroscopic shear viscosity and $G_{\infty }$ is the high-frequency shear modulus. Below $T_A$ the ratio of ${\tau }_M/{\tau }_{LC}$ increases with decreasing temperature, indicating increased atomic cooperativity as predicted by molecular dynamics simulation.

We propose a general procedure to study double integrals arising when considering wave propagation in periodic structures. This method, based on a complex deformation of the integration surface to bypass the integrands' singularities, is particularly efficient to estimate the Green's functions of such structures in the far field. We provide several illustrative examples and explicit asymptotic formulas. Special attention is devoted to the pathological cases of degeneracies, such as Dirac conical points.

Perpendicular magnetic anisotropy thin film systems are well known for their periodic magnetic stripe domain structures. In this study, we focus on investigating the behavior of [Co(3.0 nm)/Pt(0.6 nm)${\mathrm{]}}_X$ multilayers within the transitional regime from preferred in-plane to out-of-plane magnetization orientation. Particularly, we examine the sample with $X=11$ repetitions, which exhibits a remanent state characterized by a significant presence of both out-of-plane (OOP) and in-plane (IP) magnetization components, here referred to as the “tilted” stripe domain state. Vector vibrating sample magnetometry and magnetic force microscopy are used to investigate this specific sample and its unusual out-of-plane reversal behavior. Through experimental data analysis and micromagnetic simulations of the tilted magnetization system, we identify a single point of irreversibility during an out-of-plane external magnetic field sweep. This behavior is qualitatively similar to the reversal of a Stoner-Wohlfarth particle or of an IP magnetized disk with remanent vortex structure, since both show distinct points of irreversibility as well. Such a collective response to an external field is typically not observed in conventional OOP or IP systems, where the reversal process often involves independent nucleation, propagation, and annihilation of individual domains. Finally, we show that our findings are not at all restricted to Co/Pt multilayers, but are a quite general feature of transitional in-plane to out-of-plane magnetization systems.

Topological magnetic textures provide a rich variety of collective excitations. We report microwave resonant dynamics of hybrid antiskyrmion strings in a microfabricated thin plate of ${\left(\mathrm{F}{\mathrm{e}}_{0.60}\mathrm{N}{\mathrm{i}}_{0.32}\mathrm{P}{\mathrm{d}}_{0.08}\right)}_3\mathrm{P}$ at 300 K. With the aid of a micromagnetic simulation, the observed resonant peaks are identified as gyrotropic motions of hybrid antiskyrmions. The simulation reveals that the magnetization dynamics at the singularity points (Bloch points) in the hybrid antiskyrmions induces in-plane propagation of a spin wave, highlighting the internal structure as an important difference from skyrmions.

The resistance of a Josephson junction array consisting of randomly distributed lead islands on exfoliated single-layer graphene shows a broad superconducting transition to zero with an onset temperature close to the transition temperature of bulk Pb. The transition region evolves with the back-gate voltage with two peaks in the temperature derivative of the resistance. The region above the lower-temperature peak is found to be well described by the Berezinskii-Kosterlitz-Thouless model of the thermal unbinding of vortex-antivortex pairs, while that below this peak fits well with the Ambegaokar-Halperin model of thermally activated phase slip or vortex depinning. Thus, a gate-tunable crossover between interaction and pinning dominated vortices is inferred. This is elaborated in terms of free vortices as well as strong pinning sites in this highly inhomogeneous Josephson junction array.

In the pursuit of higher critical temperature of superconductivity, quasiflat electronic bands and Van Hove singularities in two dimensions (2D) have emerged as a potential approach to enhance Cooper pairing on the basis of mean-field expectations. However, these special electronic features suppress the superfluid stiffness and, hence, the Berezinskii-Kosterlitz-Thouless (BKT) transition in 2D superconducting systems, leading to the emergence of a significant pseudogap regime due to superconducting fluctuations. In the strong-coupling regime, one finds that superfluid stiffness is inversely proportional to the superconducting gap, which is the predominant factor contributing to the strong suppression of superfluid stiffness. Here we reveal that the aforementioned limitation is avoided in a 2D superconducting electronic system with a quasiflat electronic band with a strong pairing strength coupled to a deep band with weak electronic pairing strength. Owing to the multiband effects, we demonstrate a screening-like mechanism that circumvents the suppression of the superfluid stiffness. We report the optimal conditions for achieving a large enhancement of the BKT transition temperature and a substantial shrinking of the pseudogap regime by tuning the intraband couplings and the pair-exchange coupling between the two band-condensates.

We theoretically investigate high-harmonic generation (HHG) in honeycomb-lattice graphene models when subjected to a DC electric field. By integrating the quantum master equation with the Boltzmann equation, we develop a numerical method to compute laser-driven dynamics in many-electron lattice systems under DC electric current. The method enables us to treat both the weak-laser (perturbative) and intense-laser (nonperturbative) regimes in a unified way, accounting for the experimentally inevitable dissipation effects. From it, we obtain the HHG spectra and analyze their dependence on laser frequency, laser intensity, laser-field direction, and DC current strength. We show that the dynamical and static symmetries are partially broken by a DC current or staggered potential term, and such symmetry breakings drastically change the shape of the HHG spectra, especially in terms of the presence or absence of $(2n+1)\mathrm{th}$-, $2n\mathrm{th}$-, or $3n\mathrm{th}$-order harmonics ($n\in \mathbb{Z}$). The laser intensity, frequency, and polarization are also shown to affect the shape of the HHG spectra. Our findings indicate that HHG spectra in conducting electron systems can be quantitatively or qualitatively controlled by tuning various external parameters, and DC electric current is used as such an efficient parameter.

We study superfluidlike spin transport facilitated by thermal diffusion of magnetic domain walls, where the positive and negative chiralities of domain walls act as opposite topological charges. The topological charge conservation leads to algebraic decay of the spin current carried by domain walls, allowing for the transport of spin over extended distances. We demonstrate that the presence of the Dzyaloshinskii-Moriya interaction can lead to nonreciprocity in spin flow, thus effectively realizing a spin ratchet. In one scenario, the nonreciprocity arises due to diode-like behavior where the nucleation of domain walls is governed by thermal activation for one direction of spin current and by viscous injection for the other direction of spin current. We confirm our predictions by micromagnetic simulations of domain walls in TmIG nanowire.

We develop a model to describe the mixed valence regime in magic-angle twisted bilayer graphene (MATBG) using the recently developed heavy-fermion framework. By employing the large-$N$ slave-boson approach, we derive the self-consistent mean-field equations and solve them numerically. We find that the SU(8) local flat-band electron symmetry constraint moiré system exhibits mixed valence properties that are different from conventional heavy-fermion systems. We find the solutions describing the physics at the filling near the Mott insulator regime in the limit of strong Coulomb interactions between the flat-band fermions. Our model can provide additional insight into the possible microscopic origin of unconventional superconductivity in MATBG.

Magnetic topological materials hold great potential for realizing emergent quantum phenomena like the axion insulator state. This paper investigates the electronic structure, magnetotransport, and angle-resolved photoemission spectroscopy study of ${\mathrm{MnSb}}_8{\mathrm{Te}}_{13}$ single crystals. Our magnetic susceptibility experiments identify pronounced ferromagnetic transitions at temperatures ($T_1=22\mathrm{K}, T_2=12.9\mathrm{K}$, and $T_3=4\mathrm{K}$), some of which are also evident in heat capacity and electrical resistivity measurements. Our electrical resistivity measurement shows a transition at 12.7 K, with the temperature dependence of $T^{1.3}$, indicating non-Fermi liquid behavior. The Hall resistivity measurements indicate the hole-dominated behavior, which was also confirmed by angle-resolved photoemission spectroscopy measurements. Density functional theory calculations demonstrate that ${\mathrm{MnSb}}_8{\mathrm{Te}}_{13}$ is a ferromagnetic topological insulator with termination-dependent surface states. However, magnetic measurements indicate weak ferromagnetism in ${\mathrm{MnSb}}_8{\mathrm{Te}}_{13}$ due to the deficiency of Mn atoms and the disorder within the sample. Our findings establish ${\mathrm{MnSb}}_8{\mathrm{Te}}_{13}$ as a magnetic topological material with weak ferromagnetism. Further study will offer opportunities to explore the intricate interaction between magnetism and topology.

We theoretically study the inverse Faraday effect (IFE), i.e., photoinduced magnetization, in two-dimensional Rashba spin-orbit-coupled electron systems irradiated by a circularly polarized light. The quantum master (Gorini-Kossakowski-Sudarshan-Lindblad) equation enables us to accurately compute the laser-driven dynamics, taking inevitable dissipation effects into account. To find the universal features of laser-driven magnetization and its dynamics, we comprehensively investigate (i) the nonequilibrium steady state (NESS) driven by a continuous wave and (ii) ultrafast spin dynamics driven by short laser pulses. In the NESS case (i), the laser-induced magnetization and its dependence of several parameters (laser frequency, laser field strength, temperature, dissipation strength, etc.) are shown to be in good agreement with the predictions from Floquet theory for dissipative systems in the high-frequency regime. In the case (ii), we focus on ferromagnetic metal states by introducing an effective magnetic field to the Rashba model as the mean field of electron-electron interaction. We find that a precession of the magnetic moment occurs due to the pulse-driven instantaneous magnetic field and the initial phase of the precession is controlled by changing the sign of light polarization. This is well consistent with the spin dynamics observed in experiments of laser-pulse-driven IFE. We discuss how the pulse-driven dynamics are captured by the Floquet theory. Our results provide a microscopic method to compute ultrafast dynamics in many-electron systems irradiated by intense light.

With spin-layer locking, the manipulation of spin degree of freedom via perpendicular electric field can be realized in a typical antiferromagnetically coupled bilayer. In analogy to the electric control of the anomalous layer Hall effect of electron within such bilayer system, we propose here its magnon counterpart, i.e., the thermal Hall effect controlled by a perpendicular electric field. Unlike electrons, a magnon is charged neutral and its transport in solids can be driven by a thermal gradient. It also exhibits Hall response due to the intrinsic Berry curvature of magnon, analogous to the achievement in electron system. Taking bilayer $2\mathrm{H}\text{−}{\mathrm{VSe}}_2$ with both H-type stacking and interlayer antiferromagnetic coupling as a platform, we perform first-principles calculations towards the magnetic exchange coupling parameters under applied electric field perpendicular to the plane. Based on linear spin wave approximation, we then fit the magnon band structures accordingly and calculate the corresponding Berry curvature. The thermal Hall coefficient dependence on the temperature under thermal gradient can be calculated correspondingly in linear response regime. It is shown that electric field reversal is able to reverse the sign of the coefficient. These findings provide a platform for the realization of all-electric magnon spintronics.

The Casimir-Lifshitz force is calculated between a heterogeneous gapped metal surface and a silica (gold) sphere attached to an atomic force microscope (AFM) cantilever tip. We demonstrate that heterogeneous surface patches with different off-stoichiometry surface properties lead to changes in the predicted distances for a specific force. This can incorrectly be interpreted as occurrences of surface roughness.

The ground states of interacting one-dimensional metals are generically Luttinger liquids. Luttinger-liquid theory is usually considered for translation invariant systems. The Luttinger-liquid description remains valid for weak quasiperiodic modulations; however, as the quasiperiodic modulation gets increasingly strong, it is increasingly renormalized and eventually fails, as the system becomes localized. We explore how quasiperiodic modulation renormalizes the Luttinger parameter characterizing this emergent Luttinger liquid, using the renormalization of transmission coefficients across a barrier as a proxy that remains valid for general quasiperiodic modulation. We find, unexpectedly, that quasiperiodic modulation weakens the effects of short-range interactions, but enhances those of long-range interactions. We support the former finding with matrix-product numerics. We also discuss how interactions affect the localization phase boundary.

Recent experiments observe the spin-wave-Meissner-current modes in ferromagnetic insulator-superconductor heterostructures, in which the coherently excited spin waves seemingly do not decay as usual beneath the superconductor strip [Borst et al., Science 382, 430 (2023)]. We interpret this phenomenon by demonstrating that the stray magnetic field emitted by the magnetization dynamics is reflected, focused, and enhanced inside the ferromagnet by the supercurrent induced in the superconductor, such that the group velocity of spin waves is strongly enhanced. Analytical and numerical calculations based on this model predict that the coherent transport of magnons is enhanced by close to $500\%$ for yttrium iron garnet capped by superconducting NbN with a decay length exceeding millimeters. Our finding may augment the performance of magnons in quantum information and quantum transport processing.

We study the motion of a domain wall on an ultrathin magnetic film using the magneto-optical Kerr effect (MOKE). Our measurements were conducted at magnetic fields approximately $2\%$ of the depinning field where the wall creeps only via thermal activation over the pinning centers present in the sample. Our results show that this creep dynamics is highly intermittent and correlated. A localized instability triggers a cascade, akin to aftershocks following a large earthquake, where the pinned wall undergoes large reorganizations in a compact active region for a few seconds. The analysis of their scale-free statistics enables us to solve an intricate, long-standing problem: thermal avalanches exist in the creep regime and they are depinning-like even for very low magnetic field. Moreover, we show that their sizes and shapes belong to the depinning quenched Kardar-Parisi-Zhang universality class.