We present anomalous behavior of temperature-dependent photoluminescence (PL) measurements on InAs quantum dot ensembles coupled to an electron reservoir in an $n-i-p$ diode structure. When negative gate voltages are applied to the sample, an anomalous initial increase of the integrated PL signal with rising temperature is observed for the ground-state and first-excited-state emission peaks. In contrast, measurements at positive gate voltages show no such anomaly and are well described by the commonly used Arrhenius model. Unlike previous studies on uncoupled quantum dot ensembles, we show that in quantum dot diode structures the anomalous temperature dependence and its dependence on the applied bias voltage is dominated by electrons tunneling from the electron reservoir to the quantum dots. Tunneling electrons enhance the PL signal by recombining with holes stored in the quantum dots and the tunneling rate depends on temperature via the Fermi distribution in the electron reservoir. With the implementation of a rate-based tunnel coupling, we develop a modified Arrhenius model that takes the observed anomalies excellently into account. Gate voltage dependent PL measurements at 77 K are further compared to capacitance-voltage spectroscopy measurements on the same sample, supporting the proposed interpretation. The PL peak width shows a characteristic evolution as a function of temperature, which is discussed qualitatively in terms of our model.

Spin valves consisting of heterostructures of single-layer hexagonal crystal on an antiferromagnetic substrate or of bilayer hexagonal crystal intercalated between two (anti)ferromagnetic insulators, with the current-in-plane geometry, are proposed. The two-dimensional hexagonal crystals such as graphene, silicene, germanene, and stanene are modeled by the tight-binding model of honeycomb lattice. The magnetization orientation of the antiferromagnetic substrate(s) controls the band gap and topological properties of bulk, which in turn control the transport of three types of spin valve geometries: (i) the in-plane transport of bulk; (ii) the transport of topological edge states along nanoribbon with bulk gap; (iii) the transport of the chiral edge state along the domain wall. The heterostructures are investigated by a tight-binding model with an (anti)ferromagnetic exchange field, Hubbard interaction and (or) spin-orbital coupling. For the first type of spin valve geometry, the Hubbard interaction could enlarge the effective band gap of bulk, which in turn improves the sensitivity of the spin valves to the antiferromagnetic exchange field. For the second and third types of spin valve geometries, the topological phase diagrams of varying types of heterostructures with spin-orbital coupling serve as a guideline for designing the spin valve. The coexistence of the Hubbard interaction and the spin-orbital coupling could enlarge the topological gap in bulk and improve the quality of the chiral edge states at the domain walls between regions with different topological numbers.

We theoretically investigate the tunneling of two-dimensional surface polaritons (2DSPs) through nanometer-wide gaps in atomically thin crystals. For quantitatively accurate results, we developed a rigorous model based on the diffraction of 2DSPs for strongly confined surface polaritons (i.e., the polariton wavelength much shorter than the free-pace photon wavelength). We find distinctive features of the tunneling of 2DSPs. First, radiation loss during the tunneling is shown to be negligible. Second, the reflection coefficient $R$ and tunneling coefficient $T$ are shown to exhibit an anomalous logarithm singularity in their dependency on the gap width. Even for a gap size over two orders of magnitude smaller than the surface polariton wavelength, an appreciable reflection coefficient was observed in our calculation. Finally, we show that when the gap size increases, the phase of $R$ saturates very rapidly to a nontrivial value of $\pi /4$. Based on these results, we further examine resonant tunneling of 2DSP through two identical gaps separated by a distance $L$, and establish a resonance condition defined by $L\approx {\lambda }_{\mathrm{sp}}\left(4n-1\right)/8$ with a positive integer $n$.

We use series expansion methods to investigate the phase diagram of a spin-1/2 Heisenberg antiferromagnet on a diamond lattice with first- and second-neighbor interactions. Using series expansions at $T=0$, we find an apparent second-order transition from collinear Néel order to an incommensurate spiral with wave vector $(k,k,0)$ at $J_2/J_1\sim 0.18$, considerably higher than the classical value $\frac{1}{8}$. We extend the calculation to the case of tetragonal distortion, as occurs in the material ${\mathrm{CuRh}}_2{\mathrm{O}}_4$. Here we find a clear second-order transition from Néel order to a $(0,0,k)$ spiral.

Density-matrix renormalization group calculations are used to determine the ground-state phase diagram of the mixed spin-(1/2, 5/2, 1/2) Heisenberg chain whose backbone consists of regularly alternating $s=1/2$ and $S=5/2$ spins, the latter of which are coupled to additional $s=1/2$ spins providing lateral branching. The proposed magnetic structure aims to describe the main characteristics of the heterotrimetallic coordination polymer $\left[{\mathrm{Cu}}^{\mathrm{II}}{\mathrm{Mn}}^{\mathrm{II}}\left({\mathrm{L}}^1\right)\right]\left[{\mathrm{Fe}}^{\mathrm{III}}\left(\mathrm{bpb}\right){\left(\mathrm{CN}\right)}_2\right]·{\mathrm{ClO}}_4·{\mathrm{H}}_2\mathrm{O}$. The full ground-state phase diagram in the parameter space exchange anisotropy versus magnetic field unveils special critical points, at which the intermediate magnetization plateaus emergent at 3/7 and 5/7 of the saturation magnetization vanish. A detailed description of the zero-temperature magnetization process and pair entanglement entropy is accomplished with the aim to distinguish the main coupling regimes. A scaling analysis is performed to accurately locate Kosterlitz-Thouless and Gaussian critical points. In particular, we introduce a new finite-size scaling protocol to properly extract the critical parameters from the size dependence of the magnetic-field range corresponding to the magnetization plateau in the close vicinity of the Gaussian point at which two gapped phases meet.

We report an unusual enhancement of the magnetic induction in single crystals of the magnetic superconductor ${\mathrm{RbEuFe}}_4{\mathrm{As}}_4$, highlighting the interplay between superconducting and magnetic subsystems in this material. Contrary to the conventional Meissner expulsion of magnetic flux below the superconducting transition temperature, we observe a substantial boost of the magnetic flux density upon approaching the magnetic transition temperature, $T_m$. Direct imaging of the flux evolution with a magneto-optical technique, shows that the magnetic subsystem serves as an internal magnetic flux pump, drawing Abrikosov vortices from the surface, while the superconducting subsystem controls their conveyance into the bulk of the magnetic superconductor via a peculiar self-organized critical state.

Many-body localized phases may not only be characterized by their ergodicity breaking, but can also host ordered phases such as the many-body localized spin-glass (MBL-SG). The MBL-SG is challenging to access in a dynamical measurement and therefore experimentally since the conventionally used Edwards-Anderson order parameter is a two-point correlation function in time. In this work, we show that many-body localized spin-glass order can also be detected from two-site reduced density matrices, which we use to construct an eigenstate spin-glass order parameter. We find that this eigenstate spin-glass order parameter captures spin-glass phases in random Ising chains both in many-body eigenstates as well as in the nonequilibrium dynamics from a local in time measurement. We discuss how our results can be used to observe MBL-SG order within current experiments in Rydberg atoms and trapped ion systems.

Several recent works have predicted that unconventional and topological superconductivity can arise in graphene, either intrinsically or by proximity effect. Then, the analysis of the spectroscopic and transport properties in graphene would be a valuable source of information in the study of the emergent superconducting order parameter. Using Green's functions techniques, we study the transport properties of a finite size ballistic graphene layer placed between a normal state electrode and a graphene lead with proximity-induced unconventional superconductivity. Our microscopic description of such a junction allows us to consider the effect of edge states in the graphene layer and the imperfect coupling to the electrodes. The tunnel conductance through the junction and the spectral density of states feature a rich interplay between graphene's edge states, interface bound states formed at the graphene-superconductor junction, Fabry-Pérot resonances originated from the finite size of the graphene layer, and the characteristic Andreev surface states of unconventional superconductors. Within our analytical formalism, we identify the separate contribution from each of these subgap states to the conductance and density of states. Our results provide an advisable tool to determine experimentally the pairing symmetry of unconventional superconductivity that can arise in graphene.

Using the multiband $d-p$ model and unrestricted Hartree-Fock approximation, we investigate the electronic structure and spin-orbital order in three-dimensional ${\mathrm{MnO}}_3$ lattice such as realized in ${\mathrm{LaMnO}}_3$. The orbital order is induced and stabilized by particular checkerboard pattern of oxygen distortions arising from the Jahn-Teller effect in the presence of strong Coulomb interactions on $e_g$ orbitals of Mn ions. We show that the spin-orbital order can be modeled using a simple Ansatz for local crystal fields alternating between two sublattices on Mn ions, which have nonequivalent neighboring oxygen distortions in $ab$ planes. The simple and computationally very inexpensive $d-p$ model reproduces correctly nontrivial spin-orbital order observed in undoped ${\mathrm{LaMnO}}_3$. Orbital order is very robust and is reduced by $\sim 3$ % for large self-doping in the metallic regime.

We show that 1D electron states confined at twin grain boundaries in ${\mathrm{MoSe}}_2$ can be modeled by a three-orbital tight-binding model including a minimum set of phenomenological hopping terms. The confined states are robust to the details of the defect hopping model, which agrees with their experimental ubiquity. Despite a valley Chern number which is finite and opposite on both sides of the defect, there is no topological protection of the confined states. This turns out to be an essential feature to have only one confined electronic band, in agreement with experiments, instead of two, as the bulk-edge correspondence would imply. Modeling the confined state as a 1D interacting electronic system allows us to unveil a mobile quantum-impurity-type behavior at energy scales beyond the Tomonaga-Luttinger liquid with an interaction range which extends up to the lattice spacing, in excellent agreement with angle-resolved photoemission spectroscopy measurements.

Via the hierarchy of correlations, we study the strongly interacting Fermi-Hubbard model in the Mott insulator state and couple it to a Markovian environment that constantly monitors the particle numbers ${\widehat{n}}_{\mu }^{\uparrow }$ and ${\widehat{n}}_{\mu }^{\downarrow }$ for each lattice site $\mu$. As expected, the environment induces an imaginary part $\gamma$ (i.e., the decay rate) of the quasiparticle frequencies ${\omega }_{\mathbf{k}}\to {\omega }_{\mathbf{k}}-i\gamma$, and it tends to diminish the correlations between lattice sites. Surprisingly, the environment also steers the state of the system on intermediate timescales $O(1/\gamma )$ to a prerelaxed state very similar to the prethermalized state after a quantum quench (i.e., suddenly switching on the hopping rate $J$). Full relaxation or thermalization occurs via local on-site heating and takes much longer.

We find that the bilayer InSe possesses an intrinsic Rashba spin-orbit coupling and hence a spin-charge conversion effect due to the breaking of mirror symmetry. The interplay between the Rashba spin-orbit coupling and the nonparabolic Mexican hat dispersion leads to an interesting intraband Lifshitz transition and strongly amplifies the spin-charge conductivity, making it larger than that in conventional two-dimensional electron gas formed at oxide interfaces. This highlights bilayer InSe as a strong candidate for next-generation spintronic devices.

In this paper, we adopt first-principles calculations based on density functional theory and kinetic Monte Carlo simulations to investigate the adsorption and diffusion of lithium in bilayer graphene (BLG) as anodes in lithium-ion batteries. Based on energy barriers directly obtained from first-principles calculations for single-Li and two-Li intercalated BLG, a new equation was deduced for predicting energy barriers considering ${\mathrm{Li}}^{{}^{\prime }}\mathrm{s}$ interactions for multi-Li intercalated BLG. Our calculated results indicate that Li energetically prefers to intercalate within rather than adsorb outside the BLG. Additionally, lithium exists in a cationic state in the BLG. More excitingly, ultrafast Li diffusion coefficient ($\sim {10}^{-5}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) within AB-stacked BLG near room temperature was obtained, which reproduces the ultrafast Li diffusion coefficient measured in recent experiment. However, ultrafast Li diffusion was not found within AA-stacked BLG near room temperature. The analyses of potential distribution indicate that the stacking structure of BLG greatly affects its height of potential well within BLG, which directly leads to the large difference in Li diffusion. Furthermore, it is found that both the interaction among Li ions and the stacking structure cause Li diffusion within AB-stacked BLG to exhibit directional preference. Finally, the temperature dependence of Li diffusion is described by the Arrhenius law. These findings suggest that the stacking structure of BLG has an important influence on Li diffusion within BLG, and changing the stacking structure of BLG is one possible way to greatly improve Li diffusion rate within BLG. At last, it is suggested that AB-stacked BLG can be regarded as an excellent candidate for anode material in lithium-ion batteries.

A recent experiment on a 51-atom Rydberg-blockaded chain observed anomalously long-lived temporal oscillations of local observables after quenching from an antiferromagnetic initial state. This coherence is surprising as the initial state should have thermalized rapidly to infinite temperature. In this Rapid Communication, we show that the experimental Hamiltonian exhibits nonthermal behavior across its entire many-body spectrum, with similar finite-size scaling properties as models proximate to integrable points. Moreover, we construct an explicit small local deformation of the Hamiltonian which enhances both the signatures of integrability and the coherent oscillations observed after the quench. Our results suggest that a parent proximate integrable point controls the early-to-intermediate time dynamics of the experimental system. The distinctive quench dynamics in the parent model could signal an unconventional class of integrable system.

For two prototype systems, we calculate the exact exchange-correlation kernels $f_{\mathrm{xc}}(x,x^{\prime },\omega )$ of time-dependent density functional theory. $f_{\mathrm{xc}}$, the key quantity for optical absorption spectra of electronic systems, is normally subject to uncontrolled approximation. We find that, up to the first excitation energy, the exact $f_{\mathrm{xc}}$ has weak frequency dependence and a simple, though nonlocal, spatial form. For higher excitations, the spatial behavior and frequency dependence become more complex. The accuracy of the underlying exchange-correlation potential is of crucial importance.

The equation of state (EOS) of materials at warm dense conditions poses significant challenges to both theory and experiment. We report a combined computational, modeling, and experimental investigation leveraging new theoretical and experimental capabilities to investigate warm-dense boron nitride (BN). The simulation methodologies include path integral Monte Carlo (PIMC), several density functional theory (DFT) molecular dynamics methods [plane-wave pseudopotential, Fermi operator expansion (FOE), and spectral quadrature (SQ)], activity expansion (actex), and all-electron Green's function Korringa-Kohn-Rostoker (mecca), and compute the pressure and internal energy of BN over a broad range of densities and temperatures. Our experiments were conducted at the Omega laser facility and the Hugoniot response of BN to unprecedented pressures (1200–2650 GPa). The EOSs computed using different methods cross validate one another in the warm-dense matter regime, and the experimental Hugoniot data are in good agreement with our theoretical predictions. By comparing the EOS results from different methods, we assess that the largest discrepancies between theoretical predictions are $\lesssim 4\%$ in pressure and $\lesssim 3\%$ in energy and occur at ${10}^6\mathrm{K}$, slightly below the peak compression that corresponds to the $K$-shell ionization regime. At these conditions, we find remarkable consistency between the EOS from DFT calculations performed on different platforms and using different exchange-correlation functionals and those from PIMC using free-particle nodes. This provides strong evidence for the accuracy of both PIMC and DFT in the high-pressure, high-temperature regime. Moreover, the recently developed SQ and FOE methods produce EOS data that have significantly smaller statistical error bars than PIMC, and so represent significant advances for efficient computation at high temperatures. The shock Hugoniot predicted by PIMC, actex, and mecca shows a maximum compression ratio of $4.55\pm 0.05$ for an initial density of $2.26\mathrm{g}/{\mathrm{cm}}^3$, higher than the Thomas-Fermi predictions by about 5%. In addition, we construct tabular EOS models that are consistent with the first-principles simulations and the experimental data. Our findings clarify the ionic and electronic structure of BN over a broad range of temperatures and densities and quantify their roles in the EOS and properties of this material. The tabular models may be utilized for future simulations of laser-driven experiments that include BN as a candidate ablator material.