We explore quantum dynamics in Floquet many-body systems with local conservation laws in one spatial dimension, focusing on sectors of the Hilbert space which are highly polarized. We numerically compare the predicted charge diffusion constants and quantum butterfly velocity of operator growth between models of chaotic Floquet dynamics (with discrete spacetime translation invariance) and random unitary circuits which vary both in space and time. We find that for small but nonzero density of charge (in the thermodynamic limit), the random unitary circuit correctly predicts the scaling of the butterfly velocity but incorrectly predicts the scaling of the diffusion constant. We argue that this is a consequence of quantum coherence on short time scales. Our work clarifies the settings in which random unitary circuits provide correct physical predictions for nonrandom chaotic systems and sheds light into the origin of the slow down of the butterfly effect in highly polarized systems or at low temperature.

The macroscopic magnetic properties and microscopic magnetic structure of ${\mathrm{Rb}}_2{\mathrm{Mn}}_3{\left({\mathrm{MoO}}_4\right)}_3{\left(\mathrm{OH}\right)}_2$ (space group $Pnma)$ are investigated by magnetization, heat capacity, and single-crystal neutron diffraction measurements. The compound's crystal structure contains bond-alternating ${\left[{\mathrm{Mn}}_3{\mathrm{O}}_{11}\right]}^{\infty }$ chains along the $b$ axis, formed by isosceles triangles of Mn ions occupying two crystallographically nonequivalent sites (the Mn1 site on the base and Mn2 site on the vertex). These chains are only weakly linked to each other by nonmagnetic oxyanions. Both superconducting quantum interference device magnetometry and neutron diffraction experiments show two successive magnetic transitions as a function of temperature. On cooling, it transitions from a paramagnetic phase into an incommensurate phase below 4.5 K with a magnetic wave vector near ${\mathbf{k}}_1=(0,0.46,0)$. An additional commensurate antiferromagnetically ordered component arises with ${\mathbf{k}}_2=(0,0,0)$, forming a complex magnetic structure below 3.5 K with two different propagation vectors of different stars. On further cooling, the incommensurate wave vector undergoes a lock-in transition below 2.3 K. The experimental results suggest that the magnetic superspace group is $Pnma.1^{\prime }\left(0b0\right)s0ss$ for the single-$\mathbf{k}$ incommensurate phase and is $P{n}^{\prime }ma\left(0b0\right)00s$ for the two-$\mathbf{k}$ magnetic phase. We propose a simplified magnetic structure model taking into account the major ordered contributions, where the commensurate ${\mathbf{k}}_2$ defines the ordering of the $c$-axis component of the Mn1 magnetic moment, while the incommensurate ${\mathbf{k}}_1$ describes the ordering of the $ab$-plane components of both Mn1 and Mn2 moments into elliptical cycloids.

To understand the superconductivity recently discovered in ${\mathrm{Nd}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$, we carried out $\mathrm{LDA}+\mathrm{DMFT}$ (local density approximation plus dynamical mean-field theory) and magnetic force response calculations. The on-site correlation in Ni-$3d$ orbitals causes notable changes in the electronic structure. The calculated temperature-dependent susceptibility exhibits the Curie-Weiss behavior, indicating the localized character of its moment. From the low-frequency behavior of self-energy, we conclude that the undoped phase of this nickelate is Fermi-liquid-like contrary to cuprates. Interestingly, the estimated correlation strength by means of the inverse of quasiparticle weight is found to increase and then decrease as a function of hole concentration, forming a domelike shape. Another finding is that magnetic interactions in this material become two-dimensional by hole doping. While the undoped ${\mathrm{NdNiO}}_2$ has the sizable out-of-plane interaction, hole dopings strongly suppress it. This two-dimensionality is maximized at the hole concentration $\delta \approx 0.25$. Further analysis as well as the implications of our findings are presented.

We describe a formulation of the density matrix embedding theory at finite temperature. We present a generalization of the ground-state bath orbital construction that embeds a mean-field finite-temperature density matrix up to a given order in the Hamiltonian, or the Hamiltonian up to a given order in the density matrix. We assess the performance of the finite-temperature density matrix embedding on the one-dimensional Hubbard model both at half-filling and away from it, and the two-dimensional Hubbard model at half-filling, comparing to exact data where available, as well as results from finite-temperature density matrix renormalization group, dynamical mean-field theory, and dynamical cluster approximations. The accuracy of finite-temperature density matrix embedding appears comparable to that of the ground-state theory, with, at most, a modest increase in bath size, and competitive with that of cluster dynamical mean-field theory.

We present a theoretical investigation of the yet unexplored dynamics of the produced excited carriers upon irradiation of hexagonal silicon carbide (6H-SiC) with femtosecond laser pulses. To describe the ultrafast behavior of laser-induced out-of-equilibrium carriers, a real-time simulation based on density-functional theory methodology is used to compute both the hot-carrier dynamics and transient change of the optical properties. A two-temperature model (TTM) is also employed to derive the relaxation processes (i.e., thermal equilibration between carrier and lattice through carrier-phonon coupling) for laser pulses of wavelength 401 nm, duration 50 fs at normal incidence irradiation which indicate that surface damage on the material occurs for fluence $\sim 1.88\mathrm{J}\mathrm{c}{\mathrm{m}}^{-2}$. This approach of linking real-time calculations, transient optical properties, and TTM modeling, has strong implications for understanding both the ultrafast dynamics and processes of energy relaxation between carrier and phonon subsystems and providing a precise investigation of the impact of hot-carrier population in surface damage mechanisms in solids.

We report the magnetotransport properties of $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ thin flakes through gate modulation at low temperatures. Under in-plane magnetic field, a large negative magnetoresistance (MR) maintains up to 10 T, which is related to the suppression of spin scattering when the magnetic order is gradually forced into the ferromagnetic (FM) state. Under perpendicular magnetic field, a steep resistance decrease is observed around ∼3 T, corresponding to the transition from an antiferromagnetic (AFM) to a canted AFM (CAFM) state. Due to the net Berry curvature, a notable anomalous Hall effect is observed and can be effectively tuned by gate voltages. The enhanced Hall coefficient would emerge under high magnetic fields when the Fermi level is close to the charge neutral point. Moreover, a transition from negative to positive MR is obtained when increasing the magnetic field. A large linear positive MR occurs around $\sim 8\mathrm{T}$, corresponding to the CAFM-FM transition. The nonsaturated positive MR here may have a similar mechanism to the one in Weyl semimetals, revealing the strong combination between topology and magnetism in $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$.

Odd-angular momentum exciton states are dark to light in monolayers of transition-metal dichalcogenides and can be addressed only by two-photon probes. Besides, $2p$-exciton states, are expected to show a fine splitting that arises from the peculiar electronic band structure of the material, characterized by a finite Berry curvature around each valley. In this paper, we study in detail the coupling of photons to $p$-exciton states, and we find that the Rashba spin-orbit interaction or a Skyrmion in the transition-metal dichalcogenide substrate can be exploited to engineer finite optical selection rules. The basis mechanism relies on a matching of the exciton angular momentum with the winding of the Rashba spin-orbit interaction or the Skyrmion topological charge. In a photonic cavity, the coupling is enhanced due to photon confinement and the resulting polaritonic branches acquire a mixing with $2p^{\pm }$ excitons, thus, providing a useful tool to detect exciton fine-splitting and and enable novel uses of odd-parity dark excitons.

Strong excitonic effects is a very subtle issue in pristine hexagonal boron nitride (h-BN) and h-BN nanoribbons (h-BNNRs) due to large band gaps and reduced dimensionality. One of the reasons for such a large exciton binding energy (as large as 2.5 eV) is weak dielectric screening. Employing first-principles calculations in conjunction with the constrained random-phase approximation, we determine the strength of the Coulomb matrix elements for pristine h-BN and h-BNNRs with armchair and zigzag edges. Due to the nonconventional screening, the calculated off-site $U$ parameters for passivated h-BNNRs turn out to be rather sizable. Coulomb interaction is weakly screened at short distances and antiscreened at intermediate distances. Transition from screening to antiscreening takes place at a distance as low as 8 Å in narrow passivated h-BNNR. The critical distance for the onset of antiscreening in hydrogen-terminated h-BNNRs is longer than in zero-dimensional molecules and clusters, but shorter than in graphene nanoribbons and carbon nanotubes. With increasing the width of the passivated h-BNNRs from the critical point about 12.6 Å, the antiscreening effect is not observed. For completeness, on-site and long-range Coulomb interactions for metallic nonpassivated zigzag h-BNNRs are also reported.

An axion is a hypothetical elementary particle which was initially postulated to solve the charge conjugation-parity problem in particle physics. Interestingly, the axion state has emerged in the effective theory of topological insulators and has attracted extensive attention in condensed matter physics. Time-reversal or inversion symmetry constrains the axion field $\theta$ to be quantized. When both the time-reversal and inversion symmetries are broken by, say, an antiferromagnetic order, the axion field $\theta$ could become unquantized and dynamical along with magnetic fluctuations, which is termed the dynamical axion field. Here, we reveal that a wide class of topological-insulator-based dynamical axion states could be distinguished from the normal-insulator-based ones by a hidden quantity derived from the pseudospin Chern number. Motivated by recent research on the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ family of materials, we further show that such topological-insulator-based dynamical axion states can be hopefully achieved in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$-based heterostructures, which should greatly facilitate the study of axion electrodynamics in condensed matter physics.

A detailed understanding of charged defects in two-dimensional semiconductors is needed for the development of ultrathin electronic devices. Here, we study negatively charged acceptor impurities in monolayer ${\mathrm{WS}}_2$ using a combination of scanning tunneling spectroscopy and large-scale atomistic electronic structure calculations. We observe several localized defect states of hydrogenic wave function character in the vicinity of the valence band edge. Some of these defect states are bound, while others are resonant. The resonant states result from the multivalley valence band structure of ${\mathrm{WS}}_2$, whereby localized states originating from the secondary valence band maximum at $\mathrm{\Gamma }$ hybridize with continuum states from the primary valence band maximum at $K/K^{\prime }$. Resonant states have important consequences for electron transport as they can trap mobile carriers for several tens of picoseconds.

Perovskite rhodates are characterized by intermediate strengths of both electronic correlation as well as spin-orbit coupling (SOC) and usually behave as moderately correlated metals. A recent publication [Phys. Rev. B 95, 245121 (2017)] on epitaxial ${\mathrm{SrRhO}}_3$ thin films reported a bad-metallic behavior and suggested the occurrence of antiferromagnetism below 100 K. We have further studied this ${\mathrm{SrRhO}}_3$ thin film by hard x-ray photoemission spectroscopy and found a very small density of states (DOS) at the Fermi level ($E_F$), which is consistent with the previously reported bad-metallic behavior. However, the absence of DOS persists up to room temperature, which contradicts the explanation of antiferromagnetic transition at $\sim 100$ K. We also employed electronic structure calculations within the framework of density functional theory and dynamical mean-field theory. In contrast to the photoemission results, our calculations indicate metallic behaviors of both bulk ${\mathrm{SrRhO}}_3$ and the ${\mathrm{SrRhO}}_3$ thin film, and a stronger correlation effect was observed in the thin film than that in the bulk. The calculated uniform magnetic susceptibility is substantially larger in the thin film than that in the bulk. We also investigated the role of SOC and found only a moderate modulation of the band structure. Hence SOC is not expected to significantly affect the electronic correlation in ${\mathrm{SrRhO}}_3$. Extrinsic effects of finite-thickness effects beyond our calculations and localization effects may play important roles to induce the negligible spectral weight at $E_F$.

A zero-site density matrix renormalization algorithm (DMRG0) is proposed to minimize the energy of matrix product states (MPSs). Instead of the site tensors themselves, we propose to optimize sequentially the “message” tensors between neighbor sites, which contain the singular values of the bipartition. This leads to a local minimization step that is independent of the physical dimension of the site. Conceptually, it separates the optimization and decimation steps in DMRG. Furthermore, we introduce two global perturbations based on the optimal low-rank correction to the current state, which are used to avoid local minima. They are determined variationally as the MPSs closest to the one-step correction of the Lanczos or Jacobi-Davidson eigensolver. These perturbations mainly decrease the energy and are free of hand-tuned parameters. Compared to existing single-site enrichment proposals, our approach gives similar convergence ratios per sweep, while the computations are cheaper by construction. Our methods may be useful in systems with many physical degrees of freedom per lattice site. We test our approach on the periodic Heisenberg spin chain for various spins and on free electrons on the lattice.

Entanglement provides characterizing features of true topological order in two-dimensional systems. We show how entanglement of disconnected partitions defines topological invariants for one-dimensional topological superconductors. These order parameters quantitatively capture the entanglement that is possible to distill from the ground-state manifold and are thus quantized to 0 or $log2$. Their robust quantization property is inferred from the underlying lattice gauge theory description of topological superconductors and is corroborated via exact solutions and numerical simulations. Transitions between topologically trivial and nontrivial phases are accompanied by scaling behavior, a hallmark of genuine order parameters, captured by entanglement critical exponents. These order parameters are experimentally measurable utilizing state-of-the-art techniques.

The results of experimental studies of the Shubnikov–de Haas (SdH) effect in the $\left(013\right)\text{−}\mathrm{HgTe}/{\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$ quantum wells (QWs) of electron type of conductivity both with normal and inverted energy spectrum are reported. Comprehensive analysis of the SdH oscillations measured for the different orientations of magnetic field relative to the quantum well plane and crystallographic exes allows us to investigate the anisotropy of the Zeeman effect. For the QWs with inverted spectrum, it has been shown that the ratio of the spin splitting to the orbital one is strongly dependent not only on the orientation of the magnetic field relative to the QW plane but also on the orientation of the in-plane magnetic field component relative to crystallographic axes laying in the QW plane that implies the strong anisotropy of in-plane $g$-factor. In the QW with normal spectrum, this ratio strongly depends on the angle between the magnetic field and the normal to the QW plane and reveals a very slight anisotropy in the QW plane. To interpret the data, the Landau levels in the tilted magnetic field are calculated within the framework of four-band kP model. It is shown that the experimental results can be quantitatively described only with taking into account the interface inversion asymmetry.

Integration of graphene-based two-dimensional materials is essential for nanoelectronics applications. Using density-functional theory, we systematically investigate the electronic properties of vertically stacked graphene-graphitic carbon nitrides (GE/GCN). We also studied the covalently lateral stitched graphene-graphitic carbon nitrides (GE-GCN heterojunctions). The effects of perpendicular electric field on the electronic properties of six different heterostructures, i.e., (i) one layer of GE on top of a layer of ${\mathrm{C}}_n{\mathrm{N}}_m$ with $(n,m)=(3,1)$, (3,4), and (4,3) and (ii) three heterostructures ${\mathrm{C}}_n{\mathrm{N}}_m/{\mathrm{C}}_{n^{\prime }}{\mathrm{N}}_{m^{\prime }}$, where $(n,m)\ne (n^{\prime },m^{\prime })$ are elucidated. The most important calculated features are (i) the systems $\mathrm{GE}/{\mathrm{C}}_3{\mathrm{N}}_4, {\mathrm{C}}_3\mathrm{N}/{\mathrm{C}}_3{\mathrm{N}}_4, \mathrm{GE}-{\mathrm{C}}_3\mathrm{N}, \mathrm{GE}-{\mathrm{C}}_4{\mathrm{N}}_3$, and ${\mathrm{C}}_3\mathrm{N}-{\mathrm{C}}_3{\mathrm{N}}_4$ exhibit semiconducting characteristics having small band gaps of ${\mathrm{\Delta }}_0=20$, 250, 100, 100, 80 meV, respectively while (ii) the systems $\mathrm{GE}/{\mathrm{C}}_4{\mathrm{N}}_3, {\mathrm{C}}_3\mathrm{N}/{\mathrm{C}}_4{\mathrm{N}}_3$, and ${\mathrm{C}}_3\mathrm{N}-{\mathrm{C}}_4{\mathrm{N}}_3$ show ferromagnetic-metallic properties. In particular, we found that, in semiconducting heterostructures, the band gap increases nontrivially with increasing the absolute value of the applied perpendicular electric field. This work is useful for designing heterojunctions and heterostructures made of graphene and other two-dimensional materials such as those proposed in recent experiments [X. Liu and M. C. Hersam Sci. Adv. 5, 6444 (2019)].

The optical properties of triptycene molecular membranes (TMMs) under the linearly and circularly polarized light irradiation have been theoretically studied. Since TMMs have the double-layered kagome lattice structures for their $\pi$ electrons, i.e., tiling of trigonal- and hexagonal-symmetric rings, the electronic band structures of TMMs have nonequivalent Dirac cones and perfect flat bands. By constructing the tight-binding model to describe the $\pi$-electronic states of TMMs, we have evaluated the optical absorption intensities and valley selective excitation of TMMs based on the Kubo formula. It is found that absorption intensities crucially depend on both the light polarization angle and the excitation position in momentum space, i.e., the momentum and valley selective optical excitation. The polarization dependence and optical selection rules are also clarified by using group theoretical analyses.