Recently, topological flat bands and the spin Hall effect have been experimentally observed in AB-stacked ${\mathrm{MoTe}}_2/{\mathrm{WSe}}_2$ heterostructures. In this paper, we systematically study the Berry curvature effects in moiré transition metal dichalcogenide (TMD) heterobilayers. We point out that the moiré potential of the remote conduction bands would induce a sizable periodic pseudomagnetic field (PMF) on the valence band. This periodic PMF creates net Berry curvature flux in each valley of the moiré Brillouin zone. The combination of the effect of the Berry curvature and the spin-valley locking can induce the spin Hall effect being observed in the experiment. Interestingly, the valley-contrasting Berry curvature distribution generated by the PMF can be probed through shift currents, which are dc currents induced by linearly polarized light through nonlinear responses. Our work sheds light on the novel quantum phenomena induced by Berry curvature in moiré TMD heterobilayers.

Analytic continuation is an essential step in extracting information about the dynamical properties of physical systems from quantum Monte Carlo (QMC) simulations. Different methods for analytic continuation have been proposed and are still being developed. This paper explores a regularization method based on the repeated application of Tikhonov regularization under the discrepancy principle. The method can be readily implemented in any linear algebra package and gives results surprisingly close to the maximum entropy method (MaxEnt). We analyze the method in detail and demonstrate its connection to MaxEnt. In addition, we provide a straightforward method for estimating the noise level of QMC data, which is helpful for practical applications of the discrepancy principle when the noise level is not known reliably.

In this paper, we investigate the electronic band structure and optical conductivity of a ${\mathrm{Pt}}_2\mathrm{Cd}{\mathrm{Se}}_3/{\mathrm{Pt}}_2\mathrm{Hg}{\mathrm{Se}}_3$ heterobilayer system composed of two-dimensional jacutingaitelike materials. These layered crystals have shown interesting properties both in bulk as well as in single layers. By using first-principles density functional theory calculations and maximally localized Wannier functions, we show how the electronic and optical properties can be controlled by means of external electric fields. We found that such perturbations can lead to significant changes in the band structure, which are dependent on the orientation of the perpendicular field. In addition, the sign of the Berry curvature around the $K$ and $K^{\prime }$ points is dependent on the magnitude and orientation of the external electric field. We also studied the topological character of the structure and found it presents quantum valley Hall states. The sizable band gap in the valley region can be used to manipulate the valley quantum freedom. Moreover, we obtained a strong anisotropy in optical conductivity, where the out-of-plane optical absorption edge is blueshifted with respect to its in-plane counterpart and the application of electric field modifies both intensities and peak positions.

We study non-Hermitian collective dynamics of spatially separated edge carbon dimer vibrations in armchair graphene nanoribbons, mediated by coherent and dissipative coupling to nonequilibrium electron transport. We show that the indirect coupling between two dimers depends crucially on gating and source-drain bias. In particular, we analyze the competition between two distinctly different energy transfer mechanism from nonequilibrium electrons to vibrations. One is the deterministic work done by nonconservative current-induced force, and the other is stochastic Joule heating. We find that the effect of the former can be effectively tuned electrically through gating and bias. Our work suggests that armchair graphene nanoribbons could serve as promising candidates in the experimental search for signatures of nonconservative current-induced forces in nanoconductors, which remains elusive despite intense theoretical study.

The conductance of graphene nanoribbons and nanoconstrictions under the effect of a scanning gate microscopy tip is systematically studied. Using a scattering approach for noninvasive probes, the first- and second-order conductance corrections caused by the tip potential disturbance are expressed explicitly in terms of the scattering states of the unperturbed structure. Numerical calculations confirm the perturbative results, showing that the second-order term prevails in the conductance plateaus, exhibiting a universal scaling law for armchair graphene strips. For stronger tips, at specific probe potential widths and strengths beyond the perturbative regime, the conductance corrections reveal the appearance of resonances originated from states trapped below the tip. The zero-transverse-energy mode of an armchair metallic strip is shown to be insensitive to the long-range electrostatic potential of the probe. For nanoconstrictions defined on a strip, scanning gate microscopy allows to get insight into the breakdown of conductance quantization. The first-order correction generically dominates at low tip strength, while for Fermi energies associated with faint conductance plateaus, the second-order correction becomes dominant for relatively small potential tip strengths. In accordance with the spatial dependence of the partial local density of states, the largest tip effect occurs in the central part of the constriction, close to the edges. Nanoribbons and nanoconstrictions with zigzag edges exhibit a similar response as in the case of armchair nanostructures, except when the intervalley coupling induced by the tip potential destroys the chiral edge states.

We study the influence of symmetry-breaking perturbations on superconductivity in multiorbital materials, with a particular focus on an external magnetic field. We introduce the field-fitness function which characterizes the pair-breaking effects of the perturbation on a given superconducting state. For even-parity superconductors we find that this field-fitness function for an external magnetic field is one, implying that the paramagnetic response is controlled only by a generalized effective $g$ factor. For odd-parity superconductors, the interplay of the effective $g$ factor and the field-fitness function can lead to counterintuitive results. We demonstrate this for $p$-wave pairing in the effective $j=\frac{3}{2}$ electronic states of the Luttinger-Kohn model.

Momentum space entanglement entropy probes quantum correlations in interacting fermionic phases. It is very sensitive to interactions, obeying volume-law scaling in general, while vanishing in the Fermi gas. We show that the Rényi entropy in momentum space has a systematic expansion in terms of the phase space volume of the partition, which holds at all orders in perturbation theory. This permits, for example, the controlled computation of the entropy of thin shells near the Fermi wave vector in isotropic Fermi liquids and BCS superconductors. In the Fermi liquid, the thin-shell entropy is a universal function of the quasiparticle residue. In the superconductor, it reflects the formation of Cooper pairs. Momentum space Rényi entropies are accessible in cold atomic and molecular gas experiments through a time-of-flight generalization of previously implemented measurement protocols.

${\mathrm{CsPbI}}_3$ is of high interest for photovoltaic applications owing to its low band gap, provided it could be stabilized in its $\gamma$ perovskite phase. Instead, it energetically prefers to adopt a so-called yellow, $\delta$ phase, with a much larger band gap and reduced photovoltaic properties. Here, using an original constrained density functional theory method, we mimic the effect of thermalized photoexcited carriers, and show that larger concentrations in photoexcited carriers (i.e., larger optical pump fluences) effectively reduce the energy difference between the $\delta$ nonperovskite ground state and the $\gamma$ perovskite phase. Even further, the stability of the phases could be potentially reversed and therefore the $\gamma$ phase stabilized under strong illumination. We also report large photostriction, i.e., large photoinduced strain for all phases in this material, making ${\mathrm{CsPbI}}_3$ suitable for other applications such as photodriven relays and photoactuators.

We present a simple simulation model for analyzing magnetic and frictional losses of magnetic nanoparticles in viscous fluids subject to alternating magnetic fields. Assuming a particle size below the single-domain limit, we use a macrospin approach and solve the Landau-Lifshitz-Gilbert equation coupled to the mechanical torque equation. Despite its simplicity the presented model exhibits surprisingly rich physics and enables a detailed analysis of the different loss processes depending on field parameters and initial arrangement of the particle and the field. Depending on those parameters regions of different steady states emerge: a region with dominating magnetic relaxation and high magnetic losses and another region region with high frictional losses at low fields or low frequencies. The energy increases continuously even across regime boundaries up to frequencies above the viscous relaxation limit. At those higher frequencies the steady state can also depend on the initial orientation of the particle in the external field. The general behavior and special cases and their specific absorption rates are compared and discussed.

We have reported on the hysteresis and training effect of spin current in $\mathrm{Pt}/{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ heterostructures during subsequent cycles of ionic liquid gate voltage $V_g$. The inverse spin Hall effect voltage in spin pumping and spin Hall magnetoresistance exhibit diode-like behaviors in the first half cycle of $V_g$ and also show hysteresis in the first cycle of $V_g$. Both the diode-like behavior and the hysteresis become weak and even vanish in the second cycle of $V_g$ due to the training effect. The above experimental results can be well explained by the screening charge doping model, in which the charge and the local magnetic moment are asymmetrically distributed in the Pt layer. The applicability of this model is further confirmed by measurements of anisotropic magnetoresistance and ferromagnetic resonance. The diode-like behavior is attributed to interplay between the asymmetrically distributed local magnetic moment and the spin current relaxation in the Pt layer. The hysteresis and the training effect arise from the incompletely reversible process between oxidation and reduction of Pt atoms and the evolution of the surface morphology at the ionic liquid/Pt interface under electric gating. This work provides new insights to improve the functional performance of electrically controlled spin current devices.

Ferromagnet-dielectric heterostructures may possess interfacial magnetic anisotropy, which varies with the electric field created in the dielectric interlayer. Such a voltage-controlled magnetic anisotropy (VCMA) represents an efficient tool for the excitation of spin waves without the use of microwave magnetic fields. In ferromagnets with a significant magnetoelastic coupling between spins and strains, however, the magnetization precession in the spin wave induces elastic vibrations. Here we report micromagnetoelastic simulations of the coupled spin and acoustic dynamics generated in the thick Fe film brought into contact with an MgO nanolayer subjected to a microwave voltage. It is found that the electrically induced periodic modulation of VCMA gives rise to the excitation of both spin and elastic waves in the magnetostrictive Fe film. Remarkably, the magnetoelastic coupling makes it possible to generate propagating spin waves having frequencies well below the ferromagnetic resonance frequency. Furthermore, when the voltage frequency approaches a value ${\nu }^{*}$ at which the dispersion relations of pure spin and transverse elastic waves cross, the excitation of traveling magnetoelastic waves with a specific hybrid dispersion occurs in the Fe film. To explain the variety of observed phenomena, we propose a generalized dispersion relation for magnetoelastic waves, which accounts for a possible difference between the wave numbers of their magnetic and elastic components. The analysis of the simulation data also reveals that frequency dependencies of the amplitudes of magnetic oscillations and elastic vibrations display significant anomalies around the crossing-point frequency ${\nu }^{*}$, which originate from the electrically induced magnetoacoustic resonance.

Recently, honeycomb cobaltates with $3d^7$ were proposed to display Kitaev physics despite weak spin-orbit coupling. However, other theoretical and experimental works found leading XXZ Heisenberg and negligible Kitaev interactions in ${\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2$ (BCAO), which calls for further study to clarify the origin of the discrepancies. Here we derive the analytical expressions of the spin model using strong-coupling perturbation theory. With tight-binding parameters obtained with ab initio calculations for idealized honeycomb BCAO, we find that the largest intraorbital $t_{2g}-t_{2g}$ exchange path, which was assumed to be small in the earlier theory proposal, leads to a ferromagnetic (FM) Heisenberg interaction. This becomes the dominant interaction, as other $t_{2g}-e_g$ and $e_g-e_g$ contributions almost cancel each other. Exactly the same assumed-to-be-small channel also generates an antiferromagnetic Kitaev interaction, which then cancels the FM Kitaev interaction from $t_{2g}-e_g$ paths, resulting in a small Kitaev interaction. Under the trigonal distortion, the preeminent isotropic Heisenberg becomes an anisotropic XXZ model, as expected, which is the case in BCAO. However, when $t_{2g}-e_g$ and intraorbital $t_{2g}-t_{2g}$ hoppings are similar in size such as in ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$, the Kitaev interaction may become comparable to the Heisenberg interaction. A way to achieve the Kitaev cobaltates is also discussed.

We investigate the interplay of quantum one-dimensional discrete ${\mathbb{Z}}_2$ gauge fields and fermion matter near full filling in terms of deconfined fractionalized hole excitations that constitute mobile domain walls between vacua that break spontaneously translation symmetry. In the limit of strong string tension, we uncover emergent integrable correlated hopping dynamics of holes which is complementary to the constrained XXZ description in terms of bosonic dimers. We analyze numerically quantum dynamics of spreading of an isolated hole together with the associated time evolution of entanglement and provide analytical understanding of its salient features. We also study the model enriched with a short-range interaction and clarify the nature of the resulting ground state at low filling of holes and identify deconfined hole excitations near the hole filling ${\nu }^h=1/3$.

We use Majorana operators to study entanglement dynamics under random free fermion unitary evolution and projective measurements in one dimension. For certain choices of unitary evolution, namely, those which swap neighboring Majorana operators, and measurements of neighboring Majorana bilinears, one can map the evolution to the statistical model of completely packed loops with crossings (CPLC) and study the corresponding phase diagram. We generalize this model using the language of fermionic Gaussian states to a general free fermion unitary evolution acting on neighboring Majorana operators and numerically compute its phase diagram. We find that both the Goldstone and area-law phases persist in this new phase diagram, but with a shifted phase boundary. One important qualitative aspect of the new phase boundary is that even for the case of commuting measurements, the Goldstone phase persists up to a finite nonzero measurement rate. This is in contrast with the CPLC, in which noncommuting measurements are necessary for realizing the Goldstone phase. We also numerically compute the correlation length critical exponent at the transition, which we find to be near to that of the CPLC, and give a tentative symmetry-based explanation for some differences in the phase transition line between the CPLC and generalized models.

We study the impact of phonon anharmonicity on the electronic dynamics of soft materials using a nonperturbative quantum-classical approach. The method is applied to a one-dimensional model of doped organic semiconductors with low-frequency intermolecular lattice phonons. We find that anharmonicity that leads to phonon hardening increases the mobility and anharmonicity that leads to phonon softening decreases the mobility. With ab initio simulations in mind, we also test various approximations, including the use of adiabatic phonon disorder, an effective harmonic model with temperature-dependent frequencies, and the Boltzmann transport equation with second-order perturbation theory scattering rates. Overall, we find surprisingly good agreement between all methods but that accounting for phonon anharmonicity is important for accurate prediction of electronic transport including both quantitative mobility values and their qualitative temperature dependence. For the model studied, phonon lifetime effects have relatively little impact on carrier transport, but the effective frequency shift due to anharmonicity is essential. In cases with highly asymmetric, non-Gaussian disorder, an effective harmonic model cannot quantitatively reproduce mobilities or finite-frequency conductivity, and this is especially true for acoustic phonons.

In actinide-based materials, the multiplicity of $5f$ orbitals provides a rich setting to elucidate the large and outstanding issues of the competition and interplay among different channels of interactions. Among them, the dual character of $5f$ electrons has been studied in some $5f$ electron Kondo lattice compounds. Here, by using scanning tunneling microscopy/spectroscopy (STS), we present the indication of Kondo effect driven by $5f$ electrons and subatomic features of single U atoms on graphene/6H-SiC(0001), ${\mathrm{Cu}}_2\mathrm{N}/\mathrm{Cu}\left(100\right)$, and Bi(110). For all three systems, an asymmetric-dip spectral feature can be observed around the Fermi energy, which is an indication of Kondo resonance in STS. The size of the “screening cloud” for single U atoms on Bi(110) is much larger than that observed on graphene/6H-SiC(0001) and ${\mathrm{Cu}}_2\mathrm{N}/\mathrm{Cu}\left(100\right)$, indicating the $5f$ electrons of single U atoms on Bi(110) are more itinerant than that on the other two substrates. In addition to the asymmetric spectrum feature around the Fermi energy, various subatomic spectrum features are also observed from the $dI/dV$ maps of U atoms on different substrates. Further density-functional theory calculations show that these distinct subatomic features arise from the orbital selective hybridizations between U atoms and the substrates. Our results present the distinct observation of the orbital selective $5f$ electron character, indication of Kondo effect, and together with the subatomic features of individual $5f$ impurity magnetic atoms adsorbed on nonmagnetic surfaces.

Gauging a global symmetry of a system amounts to introducing new degrees of freedom whose transformation rule makes the overall system observe a local symmetry. In quantum systems there can be obstructions to gauging a global symmetry. When this happens the symmetry is dubbed anomalous. Such obstructions are related to the fact that the global symmetry cannot be written as a tensor product of local operators. In this paper we study nonlocal symmetries that have an additional structure: They take the form of a matrix product operator (MPO). We exploit the tensor network structure of the MPOs to construct local operators from them, satisfying the same group relations; that is, we are able to localize even anomalous MPOs. For nonanomalous MPOs, we use these local operators to explicitly gauge the MPO symmetry of a one-dimensional quantum state obtaining nontrivial gauged states. We show that our gauging procedure satisfies all the desired properties that the standard on-site case does. We also show how this procedure is naturally represented in matrix product states protected by MPO symmetries. In the case of anomalous MPOs, we shed light on the obstructions to gauging these symmetries.

We investigate the relaxation dynamics of equal-time correlations in the antiferromagnetic phase of the XXZ spin-1/2 chain following a global quantum quench of the anisotropy parameter. We focus, in particular, on the relaxation dynamics starting from an initial Néel state. Using state-of-the-art density-matrix renormalization group simulations, the exact solution of an effective free-fermion model, and the quench-action approach within the thermodynamic Bethe ansatz, we show that the late-time relaxation is characterized by a power-law decay $\sim t^{-3/2}$ independent of anisotropy. This is in contrast to the previously studied exponential decay of the antiferromagnetic order parameter. Remarkably, the effective model describes the numerical data extremely well even on a quantitative level if higher-order corrections to the leading asymptotic behavior are taken into account.

Magnetic excitations in layered magnetic materials that can be thinned down to the two-dimensional (2D) monolayer limit are of great interest from a fundamental point of view and for applications. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered $A$-type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response (i) through the variations of the scattered intensities, (ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and (iii) through the observation below the Néel temperature $\left(T_N\right)$ of second-order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently identified low-temperature phase, have a particular Raman scattering signature. This work demonstrates that magnetic ordering can be observed directly in the Raman scattering response of bulk CrSBr with in-plane magnetization and that it can provide unique insight into the magnetic phases encountered in magnetic layered materials.