We present experimental results where hysteresis is observed depending on the magnetic field sweep direction in the integer quantum Hall regime of a high-mobility two-dimensional electron system formed in a GaAs/AlGaAs heterostructure. We analyze the results based on the screening theory and show that the anomalous effects observed stem from the nonequilibrium processes resulting from the formation of metal-like and insulator-like regions due to direct Coulomb interactions and the dissipative nature of the Hall bar together with the scattering-influenced contacts. Furthermore, the hysteretic behavior is shown for the integer filling factors $\nu =1$, 2, and 4 and for certain fractional states at the longitudinal resistance. We argue that the nonequilibration is not only due to contacts, in contrast, but also due to the nature of the finite size dissipative Hall bar under interactions and Landau quantization.

A supercurrent on the proximitized surface of a topological insulator can cause a delocalization transition of a Majorana fermion bound to a vortex core as a zero mode. Here we study the dynamics of the deconfinement, as a manifestation of the Magnus effect (the coupling of the superflow to the velocity field in the vortex). The initial acceleration of the Majorana fermion is $\pm 2v_{\mathrm{F}}^{2}K/\hslash$, perpendicular to the Cooper pair momentum $\mathit{K}$, for a $\pm 2\pi$ winding of the superconducting phase around the vortex. The quasiparticle escapes with a constant velocity from the vortex core, which we calculate in a semiclassical approximation and compare with computer simulations.

Suppression of clustering of single-atom catalysts during chemical reaction is a long-standing challenge in heterogeneous catalysis, largely due to the prevailing design scheme that the catalytic atoms are anchored onto the supporting surfaces. Here we use first-principles approaches to establish a different design principle, where the single-atom catalytic centers are dynamically sandwiched between a porous g-${\mathrm{C}}_3{\mathrm{N}}_4/{\mathrm{MoS}}_2$ heterobilayer as a prototypical system. We show that many of the transition metals can be well stabilized as dispersive single atoms within the porous centers. Moreover, the single atoms migrate out of their sandwiched homes in ${\mathrm{O}}_2$ activation and CO oxidation, and successfully return home after the reaction is completed. In such a dynamical process the single atoms function as electronic antennas, facilitating the charge donation to or acceptance from the reactants, while effectively lowering the reaction barriers. These findings are instructive in establishing high-performance single-atom catalysts upon two-dimensional porous materials.

The bound states in the continuum (BICs) in optical metasurfaces have latterly received prominent attention for their ultrahigh quality factors and the promise that they hold for realizing lowthreshold nanolasers, high-harmonic generation, and slow-light devices. In this scenario, the flexible tuning of the BIC is at the heart of multifunctional and tunable metadevices underpinning the central role in the modulation of optical spectral responses. Most BIC-inspired works are limited to single types of BICs modes only affected by the structural perturbation without tunable functionality, while different types of BIC modes have received little attention in manipulating the spectral line shapes in optical metasurface. Here, we show that the simultaneous generation and tailored interplay of two types of BIC modes can empower the realization of tailorable spectral lineshape manipulation in all-dielectric metasurfaces. In particular, the magnetic symmetry-protected BICs and accidental BIC result from the preserved reflection symmetry and geometrical parameter perturbation, respectively. The varied asymmetric parameters and the polarization angle of the incident light are responsible for the generation and interplay of the symmetry-protected and accidental quasi-BIC modes. Additionally, the interplaying quasi-BICs enable the implementation of the dual-wavelength passive optical switches throughout the related telecom bands, and can exhibit the tunable spectral features of different types of Fano resonances and EIT analog-based slow-light effect. These results could offer exploration potential for the development of multifunction and high-performance metadevices.

Many-body localization is believed to be generically unstable in quantum systems with continuous non-Abelian symmetries, even in the presence of strong disorder. Breaking these symmetries can stabilize the localized phase, leading to the emergence of an extensive number of quasilocally conserved quantities known as local integrals of motion, or $l$ bits. Using a sophisticated nonperturbative technique based on continuous unitary transforms, we investigate the one-dimensional Hubbard model subject to both spin and charge disorder, compute the associated $l$ bits and demonstrate that the disorder gives rise to a novel form of spin-charge separation. We examine the role of symmetries in delocalizing the spin and charge degrees of freedom, and show that while symmetries generally lead to delocalization through multiparticle resonant processes, certain subsets of states appear stable.

We report on large anisotropic magnetoresistance (AMR) in surface states of an antiferromagnetic semiconductor $\mathrm{Cr}{\mathrm{Sb}}_2$. The low-temperature measurement of angle-dependent magnetoresistance (ADMR) is performed in high magnetic fields up to 24 T. At 1.4 K, where the surface conduction is dominant, ADMR exhibits clear twofold symmetry consistent with AMR due to magnetic-field-induced change of antiparallel magnetic structure. The AMR magnitude reaches 9.3% despite the small angle dependence of the net magnetic moments, suggesting strong spin-orbit interaction in the surface conduction layer.

We examine the mechanical rotation of a levitated magnetic particle that is induced by ferromagnetic resonance under microwave irradiation. We show that two stable solutions appear in a certain range of parameters by bifurcation when the rotation frequency is comparable to the microwave frequency. This phenomenon originates from the coexistence of the Barnett and the Einstein–de Haas effects. We also reveal that this measurement is sensitive to the strength of the spin-rotation coupling. Our work provides a platform for accessing a microscopic relaxation process from spin to macroscopic rotation.

Majorana zero modes form as intrinsic defects in an odd-orbital one-dimensional superconductor, thus motivating the search for such materials in the pursuit of Majorana physics. Here, we present combined experimental results and first-principles calculations which suggest that quasi-one-dimensional ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ may be such a superconductor. Using inelastic neutron scattering we probe the dynamic spin susceptibilities of ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ and ${\mathrm{K}}_2{\mathrm{Mo}}_3{\mathrm{As}}_3$ and show the presence of antiferromagnetic spin fluctuations in both compounds. Below the superconducting transition, these fluctuations gap in ${\mathrm{K}}_2{\mathrm{Mo}}_3{\mathrm{As}}_3$ but not in ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$. Using first-principles calculations, we show that these fluctuations likely arise from nesting on one-dimensional features of the Fermi surface. Considering these results we propose that while ${\mathrm{K}}_2{\mathrm{Mo}}_3{\mathrm{As}}_3$ is a conventional superconductor, ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ is likely a spin triplet, and consequently a topological superconductor.

Ab initio and continuum model studies predicted that the $\mathrm{\Gamma }$ valley transition metal dichalcogenide (TMD) homobilayers could simulate the conventional multiorbital Hubbard model on the moiré honeycomb lattice. Here, we perform the Wannierization starting from the continuum model and show that a more general moiré Kanamori-Hubbard model emerges, beyond the extensively studied standard multiorbital Hubbard model, which can be used to investigate the many-body physics in the $\mathrm{\Gamma }$ valley TMD homobilayers. Using the unrestricted Hartree-Fock and Lanczos techniques, we study these half-filled multiorbital moiré bands. By constructing the phase diagrams we predict the presence of an antiferromagnetic state and in addition we found unexpected and dominant states, such as a $S=1$ ferromagnetic insulator and a charge density wave state. Our theoretical predictions made using this model can be tested in future experiments on the $\mathrm{\Gamma }$ valley TMD homobilayers.

Recent experimental discovery of flavor symmetry breaking metallic phases in Bernal-stacked bilayer graphene points to the strongly interacting nature of electrons near the top (bottom) of its valence (conduction) band. Superconductivity was also observed in between these symmetry breaking phases when the graphene bilayer is placed under a small in-plane magnetic field or in close proximity to a monolayer ${\mathrm{WSe}}_2$ substrate. Here we address the correlated nature of the band edge electrons and obtain the quantum phase diagram of their many-body ground states incorporating the effect of proximity induced spin-orbit coupling. We find that in addition to the spin/valley flavor polarized half and quarter metallic states, two types of intervalley coherent phases emerge near the phase boundaries between the flavor polarized metals. Both spin-orbit coupling and in-plane magnetic field disfavor the spin-unpolarized valley coherent phase. Our findings suggest possible competition between intervalley coherence and superconducting orders, arising from the intriguing correlation effects in bilayer graphene in the presence of spin-orbit coupling.

Analytic mathematical models for the static spin ($G_{-}$) and density ($G_{+}$) local field factors for the uniform electron gas (UEG) as functions of wave vector and density are presented. These models closely fit recent quantum Monte Carlo (QMC) data and satisfy exact asymptotic limits. A simple functional form for $G_{-}$ is developed; the same functional form parametrized for $G_{+}$ yields an improvement over previous work. The QMC-computed $G_{\pm }$ are consistent with a rapid crossover between theoretically derived small-$q$ and large-$q$ expansions of $G_{\pm }$. These expansions are completely determined by $r_{\mathrm{s}}$, the UEG correlation energy per electron, and the UEG on-top pair distribution function. We demonstrate their utility by computing uniform electron gas correlation energies over a range of densities. These models, which hold over an extremely wide range of densities, are recommended for use in practical time-dependent density functional theory calculations of simple metallic systems. A revised model of the spin susceptibility enhancement is developed that fits QMC data, and does not show a ferromagnetic instability at low density.

Motivated by the pseudogap state of the cuprates, we introduce the concept of an “exceptional” van Hove singularity that appears when a strong electron-electron interaction splits an otherwise simply connected Fermi surface into multiply connected pieces. The singularity describes the touching of two pieces of the split Fermi surface. We show that this singularity is proximate to a second-order van Hove singularity, which can be accessed by tuning a dispersion parameter. We argue that, in a wide class of cuprates, the endpoint of the pseudogap is accessed only by triggering the exceptional van Hove singularity. The resulting Lifshitz transition is characterized by enhanced specific heat and nematic susceptibility, as seen in experiments.

From the ultraviolet to the mid-infrared region, light-matter interaction mechanisms in semiconductors progressively shift from electronic transitions to phononic resonances and are affected by temperature. Here, we present a unified temperature-dependent treatment of both electrons and phonons entirely from first principles, enabling the prediction of a full-spectrum dielectric function with ${\mathrm{CeO}}_2$ as the prototype material. At elevated temperatures, ab initio molecular dynamics is employed to find thermal perturbations to electronic structures and construct effective force constants describing potential energy surface. Four-phonon scattering and phonon renormalization are included in an integrated manner in this approach. Our first-principles-calculated refractive index of ${\mathrm{CeO}}_2$ agrees well with measured data from literature and our own temperature-dependent ellipsometer experiment.

We present a model of diamagnetic shifts for two-dimensional Wannier-Mott excitons in out-of-plane magnetic fields, including environmental dielectric effects. We indicate the reasons for the magnetic-field-induced increase of exciton mass and size. In the weak-field limit, we deduce the diamagnetic coefficient and explain why its value is significantly different between excitonic states. Our results agree well with experimental data.

The use of dissipation for the controlled creation of nontrivial quantum many-body correlated states is of much fundamental and practical interest. What is the result of imposing number conservation, which, in closed system, gives rise to diffusive spreading? We investigate this question for a paradigmatic model of a two-band system, with dissipative dynamics aiming to empty one band and to populate the other, which had been introduced before for the dissipative stabilization of topological states. Going beyond the mean-field treatment of the dissipative dynamics, we demonstrate the emergence of a diffusive regime for the particle and hole density modes at intermediate length- and timescales, which, interestingly, can only be excited in nonlinear response to external fields. We also identify processes that limit the diffusive behavior of this mode at the longest length- and timescales. Strikingly, we find that these processes lead to a reaction-diffusion dynamics governed by the Fisher-Kolmogorov-Petrovsky-Piskunov equation, making the designed dark state unstable towards a state with a finite particle and hole density.

We have investigated the photoexcited transient responses of stripe-ordered phase in a cuprate superconductor, ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ ($x=0.12$), using optical-pump terahertz (THz)-probe spectroscopy. Upon the near-infrared photoexcitation with the electric field polarized along the $c$ axis, a clear plasma edge appears in the THz reflection spectrum along the $c$ axis with its position nearly coinciding with the Josephson plasma resonance of similarly doped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ ($x=0.125$) in the low-temperature superconducting phase. The appearance of a light-induced plasma edge sustains up to the onset temperature of the charge-stripe order, indicating the inherent interplay between the light-induced phase and the charge-stripe order. The optical conductivity spectrum of the light-induced state is mostly reproduced by the Drude model with a scattering rate as small as a few meV, and its imaginary part does not exhibit $\frac{1}{\omega }$-divergence behavior in any temporal region after the photoexcitation. We discuss the possible origin of the observed coherent interlayer transport behavior as manifested by the narrow Drude response in the THz reflectivity along the $c$ axis.

Using an atomistic tight-binding model, we investigate the characteristics of a Josephson junction formed by monolayers of ${\mathrm{MoS}}_2$ sandwiched between Pb superconducting electrodes. We derive and apply Green's function–based formulation to compute the Josephson current as well as the local density of states in the junction. Our analysis of diagonal and off-diagonal components of the local density of states reveals the presence of triplet superconducting correlations in the ${\mathrm{MoS}}_2$ monolayers and spin-polarized subgap (Andreev bound) states. Our formulation can be extended to other systems where atomistic details and large scales are needed to obtain accurate modeling of Josephson junction physics.

The coexistence of Dirac cones and Van Hove singularities (VHSs), as the notable feature on prominent electronic band structure in recently hot-topic Lieb lattice and twisted graphene superlattice materials, has recently drawn tremendous attention since it offers an ideal platform for realizing correlation-driven electronic states (e.g., superconductivity and topological state). Here, we have identified two two-dimensional (2D) crystals, namely ${\mathrm{C}}_4\mathrm{Se}$ and ${\mathrm{C}}_5\mathrm{Se}$, which exhibit the coexistence of Dirac cones and VHSs. Based on ab initio calculations and the Bardeen-Cooper-Schrieffer theory, we investigated the electron-phonon coupling and possible superconductivity in both structures. The results indicate that ${\mathrm{C}}_4\mathrm{Se}$ possesses intrinsic superconducting states, whereas ${\mathrm{C}}_5\mathrm{Se}$ exhibits tunable superconductivity when doped. Their superconducting critical temperature ($T_c$) can reach up to 11.6 and 11.2 K, respectively, surpassing the majority of 2D superconductors. Besides, we uncovered an approximate Dirac cone in ${\mathrm{C}}_6\mathrm{Se}$ with a small band gap of 0.17 eV. Via the application of a biaxial compressive strain, remarkably, the ${\mathrm{C}}_6\mathrm{Se}$ can be transformed into a topological insulator. These findings highlight the potential of carbon-rich C-Se 2D crystals as a promising platform for investigating fascinating band structures and physical states, thus advancing our comprehension of 2D crystals.

We numerically investigate the characteristics of the long-time dynamics of a single-site wave-packet excitation in a disordered and nonlinear Su-Schrieffer-Heeger model. In the linear regime, as the parameters controlling the topology of the system are varied, we show that the transition between two different topological phases is preceded by an anomalous diffusion, in contrast to Anderson localization within these topological phases. In the presence of onsite nonlinearity this feature is lost due to mode-mode interactions. Direct numerical simulations reveal that the characteristics of the asymptotic nonlinear wave-packet spreading are the same across the whole studied parameter space. Our findings underline the importance of mode-mode interactions in nonlinear topological systems, which must be studied in order to define reliable nonlinear topological markers.

The accurate computation of forces and other energy derivatives has been a long-standing challenge for quantum Monte Carlo methods. A number of technical obstacles contribute to this challenge. We discuss how these obstacles can be removed with the auxiliary-field quantum Monte Carlo (AFQMC) approach. AFQMC is a general, high-accuracy, many-body total-energy method for molecules and solids. The implementation of back-propagation for pure estimators allows direct calculation of gradients of the energy via the Hellmann-Feynman theorem. A planewave basis with norm-conserving pseudopotentials is used for the study of periodic bulk materials. Completeness of the planewave basis minimizes the effect of so-called Pulay terms. The ionic pseudopotentials, which can be incorporated in AFQMC in exactly the same manner as in standard independent-electron methods, regulate the force and stress estimators and eliminate any potential divergence of the Monte Carlo variances. The resulting approach allows applications of full geometry optimizations in bulk materials. It also paves the way for many-body computations of the phonon spectrum in solids.