The use of strong periodic light irradiation to drive Bloch state evolution and another weak light to probe this dynamic process is an effective yet underexplored strategy. Here, based on the first-principles calculations and Floquet theory, we systematically study the electronic structure evolution in a noncentrosymmetric system under a circularly polarized pump light. This process is analyzed using the Bernevig-Hughes-Zhang model, in which we elucidate that the pump light renormalizes the hopping integral and acts as an effective spin-orbit coupling, so that it reduces the system band gap. Using a monolayer BiSb as an exemplary material platform, we show that its band gap would close and reopen as the pump light intensity increases, corresponding to a topological phase transition (TPT) with distinct Chern numbers. We further propose that a weak probe light could capture such a TPT through second-order nonlinear optical responses, such as the bulk photovoltaic effect (BPVE) and second harmonic generation (SHG) process. Both the BPVE and SHG are largely enhanced in the Floquet-induced topologically nontrivial state. Importantly, the shift current flips direction under the TPT, offering an exquisite characteristic tool with high sensitivity to characterize the Chern number. Our work proposes an all-optical strategy to pump and probe the TPT in noncentrosymmetric systems, providing potential design strategy of dynamic nonlinear optical devices.

The phenomenon of quantum many-body scars has received widespread attention both in theoretical and experimental physics in recent years due to its unique physical properties. In this paper, based on the su(2) algebraic relations, we propose a general method for constructing scar models by combining simple modules. This allows us to investigate many-body scar phenomena in high-spin systems. We numerically verify the thermalization and nonintegrability of this model and demonstrate the dynamical properties of the scar states. We also provide a theoretical analysis of the properties of these scar states. For spin-1 case, we find that our 1D chain model reduces to the famous PXP model [C. J. Turner et al., Phys. Rev. B 98, 155134 (2018)] under special parameter conditions. In addition, due to the continuous tunability of the parameters, our model also enables us to investigate the transitions of quantum many-body scar phenomena from nonintegrable to integrable system.

Previous investigations have suggested that the simplest spin-orbital model on the simplest frustrated lattice can host a nematic quantum spin-orbital liquid state. Namely, the orbital degeneracy of the SU(4) Kugel-Khomskii model tends to enhance quantum fluctuations and stabilize a quantum spin-orbital liquid exhibiting stripy features on the triangular lattice, as revealed by the state-of-the-art method of the density matrix renormalization group boosted by Gutzwiller projected wave functions. In this work, using the variational quantum Monte Carlo method, we study several spin-orbital liquid states, including a uniform $\pi$-flux state, three stripy states, and a plaquette state, on the $L\times L$ torus up to $L=24$. It turns out that one of these stripy states, called the “stripe-II” state, is energetically favored. This ground state breaks the $C_6$ symmetry of the lattice, resulting in a reduced $C_2$ symmetry and doubled unit cells while preserving the SU(4) spin-orbital rotation symmetry. Such a nematic quantum spin-orbital liquid state can be characterized by a parton Fermi surface (FS) consisting of open orbits in the Brillouin zone, in contrast to the circular FS of the uniform $\pi$-flux state.

Recent experiments on ultracold dipoles in optical lattices open exciting possibilities for the quantum simulation of extended Hubbard models. When considered in one dimension, these models present at unit filling a particularly interesting ground-state physics, including a symmetry-protected topological phase known as Haldane insulator. We show that the tail of the dipolar interaction beyond nearest-neighbors, which may be tailored by means of the transversal confinement, does not only modify quantitatively the Haldane insulator regime and lead to density waves of larger periods, but results as well in unexpected insulating phases. These insulating phases may be topological or topologically trivial, and are characterized by peculiar correlations of the site occupations. These phases may be realized and observed in state-of-the-art experiments.

Based on a tight-binding model for the electron system, we investigate the transfer of energy, momentum, and angular momentum mediated by electromagnetic fields among buckminsterfullerene (${\mathrm{C}}_{60}$) and graphene nanostrips. Our nonequilibrium Green's function approach enables calculations away from local thermal equilibrium where the fluctuation-dissipation theorem breaks down. For example, the forces between ${\mathrm{C}}_{60}$ and current-carrying nanostrips are predicted. It is found that the presence of current enhances the van der Waals attractive forces. For two current-carrying graphene strips rotated at some angle, the fluctuational force and torque are much stronger at the nanoscale compared to that of the static Biot-Savart law.

We present a theoretical formalism to investigate quantum spin transport in a two-dimensional metal/ferromagnetic insulator (FI) heterostructure in the presence of disorder. The formalism is based on the full counting statistics (FCS) within coherent potential approximation (CPA), which is capable of calculating the disorder average of an arbitrary number of Green's functions. Due to the convolutional structure of the self-energy of the FI lead, the conventional FCS-CPA formalism breaks down in our system. We propose two solutions to solve this problem. We numerically examine the formalism by calculating the average spin conductance in a disordered nonmagnetic metal/FI (NM/FI) heterostructure and apply it to a disordered altermagnetic metal/FI (AM/FI) heterostructure. The FCS-CPA results exhibit excellent agreement with brute force calculations in weak disorders. In AM/FI systems, the spin transport is enhanced in weak disorders and suppressed in strong disorders. Stronger anisotropic hopping suppresses the spin transport in AM/FI systems. The average spin conductance is notably sensitive to the spin polarization of AM states. The methods proposed here are also applicable to the convolutional self-energy in electron-phonon coupling systems.

The ground states of twisted bilayer graphene (TBG) at chiral and flat-band limit with integer fillings are known from exact solutions, while their dynamical and thermodynamical properties are revealed by unbiased quantum Monte Carlo (QMC) simulations. However, to elucidate experimental observations of correlated metallic, insulating, and superconducting states and their transitions, investigations on realistic, or nonchiral cases are vital. Here we employ momentum-space QMC method to investigate the evolution of correlated states in magic-angle TBG away from chiral limit at charge neutrality with polarized spin/valley, which approximates to an experimental case with filling factor $\nu =-3$. We find that the ground state evolves from quantum anomalous Hall insulator into an intriguing correlated semimetallic state possessing heavy-fermion features as AA hopping strength reaches experimental values. Such a state resembles the recently proposed heavy-fermion representations with localized electrons residing at AA stacking regions and delocalized electrons itinerating via AB/BA stacking regions. The spectral signatures of the localized and itinerant electrons in the heavy-fermion semimetal phase are revealed, with the connection to experimental results being discussed.

Motivated by recent experiments on Si/SiGe quantum wells with a co-design of high electron mobility and large valley splitting [Paquelet Wuetz et al., Nat. Commun. 14, 1385 (2023); Esposti et al., arXiv:2309.02832 [cond-mat.mes-hall]], suitable for a Si-based spin qubit quantum computing platform, we examine the role of disorder by theoretically calculating mobility and quantum mobility from various scattering mechanisms and their dependence on the electron density. At low electron densities $n_e<4\times {10}^{11}{\mathrm{cm}}^{-2}$, we find that mobility is limited by remote Coulomb impurities in the capping layer, whereas interface roughness becomes the significant limiting factor at higher densities. We also find that alloy disorder scattering is not a limiting mechanism in the reported high-mobility structures. We estimate the critical density of the disorder-driven low-density metal-insulator transition using the Anderson-Ioffe-Regel localization criterion and qualitatively explain the breakdown of the Boltzmann-Born theory at low densities. We also estimate the critical density by considering inhomogeneous density fluctuations induced by long-range Coulomb disorder in the system, and find a larger critical density compared to the one obtained from the Anderson-Ioffe-Regel criterion. For quantum mobility, our calculation suggests that remote and distant background impurities are likely the limiting scattering sources across all densities. Future measurements of quantum mobility should provide more information on the distribution of background impurities inside the SiGe barriers. Moreover, we extend our theoretical analysis to the effect of quantum degeneracy on transport properties and predict the mobility and the critical density for the metal-insulator transition in spin-polarized high-mobility structures under an external parallel magnetic field.

${\mathrm{CaSb}}_2$ is the Dirac line-nodal material that exhibits a superconducting (SC) transition at 1.7 K. In spite of its conventional SC state at ambient pressure, the transition temperature $T_{\mathrm{c}}$ shows a peak structure against hydrostatic pressure. We performed ac magnetic susceptibility and ${}^{123}\mathrm{Sb}$ nuclear quadrupole resonance (NQR) measurements on single-crystalline ${\mathrm{CaSb}}_2$ under pressures up to 2.08 GPa. $T_{\mathrm{c}}$ monotonically increased in this pressure region, which is consistent with a previous study. We observed continuous broadening of the NQR spectrum against pressure, which is a sign of unique compression behavior of the lattice. In the normal state, the nuclear spin-lattice relaxation rate $1/T_1$ is proportional to temperature in all pressure values, typical of a metal. However, $1/T_{1}T$ in the normal state is independent of pressure, indicating that the density of states at the Fermi energy $N\left(E_{\mathrm{F}}\right)$, which is one of the parameters governing $T_{\mathrm{c}}$, is insensitive to pressure. From these results, we conclude that $N\left(E_{\mathrm{F}}\right)$ does not govern the origin of the enhancement in $T_{\mathrm{c}}$. This is unusual for a weak electron-phonon coupling superconductor. In the SC state, we revealed that the SC gap becomes larger and more isotropic under pressure.

Isotope effects on phonon properties and transport have been predicted and observed for decades. However, despite the crucial impact of electron-phonon interactions, the effect of isotopes on electron transport remains largely unexplored. Here, by using first-principles calculations, we theoretically predict that the electron mobility of lithium hydride (LiH) can increase by up to ∼100% as ${}^3\mathrm{H}$ is replaced with ${}^1\mathrm{H}$. This remarkable phenomenon is primarily attributed to the isotope engineering of the Fröhlich interaction by the mass-induced line shift of the longitudinal optical (LO) phonons. Notably, the isotope-dependent absorption of LO phonons dominates while the isotope-insensitive emission process is mostly suppressed due to energy conservation. We further propose general guidelines for evaluating isotope effects on carrier transport in different materials.

In this work, we demonstrate a simple yet effective procedure for identifying the exotic tetrahedral triple-Q magnetic ordering over the domain averaged collinear single-Q magnetic state for the triangular antiferromagnet ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$. Our density functional theory (DFT) calculations show that the hyperfine magnetic field exhibits a significant anisotropic dependence on the angle between the spin direction and the $c$-axis, which means that the atoms with different spin directions in the triple-Q state can be divided into two subgroups with a ratio of 1:3 that can be distinguished by local probing methods. Mössbauer spectroscopy measurements on ${\left({\mathrm{Co}}_{0.99}{}^{57}\mathrm{Fe}_{0.01}\right)}_{1/3}{\mathrm{NbS}}_2$ crystals confirm exactly our DFT predictions and thus give possible evidence of the tetrahedral triple-Q magnetic state. These results provide important insights into the magnetic ground state of ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$, which shall shed light on the understanding of the anomalous Hall effect in ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$ and other related materials.

The high-temperature limit of interacting spins is usually not associated with ordering or critical phenomena. Nevertheless, spontaneous fluctuations of a local spin polarization at equilibrium have nontrivial dynamics even in this limit. Here, we demonstrate that the spin noise power spectrum of these fluctuations can undergo discontinuous changes as a function of an external magnetic field. As a simple illustration, we consider a model of Ising-like long-range spin-spin interactions with a transverse magnetic field as a control parameter. This system undergoes a phase transition associated with disappearance of the noise power peak responsible for the most detrimental decoherence effect of the interactions.

The past few years have seen an increased interest in nonreciprocal phenomena in superconductors, especially the superconducting diode effect (SDE) characterized by the nonreciprocity of the critical current $\mathrm{\Delta }{J}_{\mathrm{c}}$. Contrary to the fundamental and practical significance of the SDE, the precise underlying mechanism remains unclear. In this paper, we investigate the impact of an orbital effect on the intrinsic SDE in a bilayer superconductor with Rashba spin-orbit coupling and an in-plane magnetic field. We show that a small orbital effect leads to the sign reversal of $\mathrm{\Delta }{J}_{\mathrm{c}}$ and a crossover of the helical superconducting state at a lower magnetic field than the monolayer superconductor. On the other hand, a large orbital effect induces a decoupling transition, stabilizing a finite momentum Cooper pairing state called the orbital Fulde-Ferrell-Larkin-Ovchinnikov state, and results in the drastic change of the SDE. Owing to the orbital effect, the field dependence of the SDE may show oscillations several times. The results shed light on the mechanism of the SDE in atomically thin multilayer superconductors.

Investigating the shock-induced structural phase transition (PT) in Al is of paramount interest due to its extensive use in numerous dynamic compression experiments. In this paper, we report nonequilibrium molecular dynamics simulation of shock compression in single-crystal Al to unfold structural PT at the atomic scale. Study along three major crystallographic orientations reveals that shock-induced $\text{fcc}\to \text{hcp}$ and $\text{fcc}\to \text{bcc}$ transitions are initiated at 18.8 and 30 GPa for the [001] direction and 32.2 (38) and 44 (46.1) GPa for the [110] ([111]) directions, respectively. Interestingly, these transition pressures are significantly lower than the values reported in the static compression experiment of Akahama et al. [Phys. Rev. Lett. 96, 045505 (2006)] and the ramp compression experiment of Polsin et al. [Phys. Rev. Lett. 119, 175702 (2017)]. Signatures of PT are identified from radial distribution function and virtual x-ray diffraction patterns. Domains of different phases are manifested in the pressure-temperature diagram of the principal Hugoniot.

Knowledge of the local coordination environment around atomic species in functional materials is critical for understanding their mechanisms of operation. Heterogeneous mixtures of metal complexes are ubiquitous in catalysts, ionic liquids, molten salts, biological enzymes, and geochemical systems, among many others. Extracting information from ensemble-average measurements about the structural and compositional descriptors of each type of coordination complex comprising the mixture is not generally possible, especially when they possess multimodal bond-length distributions. We developed a method that enables the mapping of an x-ray absorption spectrum on the radial distribution function describing the average environment of the metal ions. The supervised neural network based method utilizes an objective training set, for which the choice of the local structural motifs is completely agnostic to the theoretically expected structure and dynamics of the modeled system. The method was validated using first-principles modeling of structural dynamics of nickel complexation in molten salts, and it applies to a large class of heterogeneous systems, including those studied under in situ and operando conditions.

It has recently been shown that giant quantum oscillations above the energy barrier (GQOAB) of a spin $S$ can be coherently induced by the simultaneous application of $2S$ alternating fields (shaped field) associated with successive level separations [Phys. Rev. Lett. 131, 066701 (2023)]. We begin the present paper with a more detailed study of the properties of GQOAB, such as the dependence of their frequency on the value of the anisotropy constant or on that of the amplitude of the alternating fields. We then extend the concept of GQOAB to the case where these ac-fields are applied, not simultaneously, but sequentially, showing that such a protocol also leads to coherent GQOAB but with a number of differences that are discussed in detail. We conclude with a classical approach of this problem showing that “giant classical oscillations above the barrier (GCOAB)” can also be designed at zero Kelvin.

Recent research has revealed remarkable properties of the two-dimensional (2D) van der Waals layered crystal CrSBr, which is both a semiconductor and an $A$-type antiferromagnet. Here we show the role of strong magnetoelastic coupling in the generation and propagation of coherent magnons in CrSBr. Time- and spatially resolved magneto-optical Kerr effect microscopy reveals two time-varying transient strain fields induced by out-of-plane transverse and in-plane longitudinal lattice displacements. These transient strain fields launch coherent wavepackets of magnons, optical and acoustic, at $24.6\pm 0.8$ and $33.4\pm 0.5\mathrm{GHz}$, respectively. These findings suggest mechanisms for controlling and manipulating coherent magnons from distinct magnetoelastic couplings in this 2D van der Waals magnetic semiconductor.

The Anderson impurity model is a paradigmatic example in the study of strongly correlated quantum systems and describes an interacting quantum dot coupled to electronic leads. Here we investigate its dynamics following a quantum quench based on matrix product state simulations. We examine the behavior of its impurity magnetization. Its relaxation allows us to extract the predicted scaling of the Kondo temperature as a function of the impurity-lead hybridization and quantum dot repulsion. Additionally, our simulations provide estimates of the currents in the nonequilibrium quasisteady state appearing after the quench. Through their values, we examine the dependence of the conductance on the voltage bias $V_b$ and on the impurity chemical potential $V_g$, which displays a zero-bias Kondo peak. Our results are relevant for transport measurements in Coulomb blockaded devices, and, in particular, in quantum dots induced in nanowires.