Motivated by the recent success of realizing the topologically ordered ground state of the exactly solvable toric code model by a quantum circuit on the real quantum device [Satzinger et al., Science 374, 1237 (2021)], here we propose a parametrized quantum circuit (PQC) with the same real-device-performable optimal structure to represent quantum loop gas states with adjustably weighted loop configurations. Combining such a PQC with the variational quantum eigensolver, we obtain the accurate quantum circuit representation for the toric code model in an external magnetic field with any field strength, where the system is not exactly solvable. The topological quantum phase transition in this system is further observed in the optimized circuits by measuring the magnetization and topological entanglement entropy.

The ab initio theory of charge transport in semiconductors typically employs the lowest-order perturbation theory in which electrons interact with one phonon (1ph). This theory is accepted to be adequate to explain the low-field mobility of nonpolar semiconductors but has not been tested extensively beyond the low-field regime. Here, we report first-principles calculations of the electric field dependence of the electron mobility of Si as described by the warm electron coefficient $\beta$. Although the 1ph theory overestimates the low-field mobility by only around 20%, it overestimates $\beta$ by over a factor of two over a range of temperatures and crystallographic axes. We show that the discrepancy in $\beta$ is reconciled by the inclusion of on-shell iterated two-phonon (2ph) scattering processes, indicating that scattering from higher-order electron-phonon interactions is non-negligible even in nonpolar semiconductors. Further, a $\sim 20\%$ underestimate of the low-field mobility with 2ph scattering suggests that nontrivial cancellations may occur in the perturbative expansion of the electron-phonon interaction.

The thermodynamic properties of warm dense hydrogen, such as the equation of state (EOS) and sound velocity, affect our understanding of the evolution and interior structures of gas giant planets. However, for this low-$Z$ gas, obtaining the EOS and sound velocity experimentally under relevant planetary conditions is challenging because the extremely warm states are difficult to reach, characterize, and interrogate. Here, the multishock compression technique is used to generate the thermodynamic states of warm dense hydrogen. This provides a dynamic loading from shock adiabatic to quasi-isentropic compressions, covering wide pressure and density ranges of 0.02–95 GPa and $0.01–0.64 \mathrm{g}/{\mathrm{cm}}^3$, which enables us to determine the EOS and infer the high-pressure sound velocities of warm dense hydrogen relevant to planetary interiors. The data obtained in this way are comprehensively compared with several important theoretical models for astrophysics applications. The present experiments provide desirable principal- and off-Hugoniot states for revisiting the thermodynamic space of existing experimental data. These observations and thermodynamic states may be important in guiding future theoretical developments and constructing interior structure models for gas giant planets.

In the ${\mathrm{Ca}}_3{\mathrm{Co}}_2{\mathrm{O}}_6$ (CCO) system, the large contribution of the orbital moment to the magnetization and the strong magnetocrystalline anisotropy (MCA) are considered to give rise to the Ising magnetism. In this study, the dominant role of both spin-orbit-coupling (SOC) and crystal-field (CF) effects behind this Ising character of magnetism is qualitatively elucidated from the temperature and field dependence of magnetization in the presence of hydrostatic pressures up to 1.04 GPa in a CCO single crystal (SC). The local trigonal prismatic environment is compressed with the application of high pressure, resulting in higher trigonal CF as compared to ambient conditions. It reduces the effect of SOC due to the initiation of orbital quenching that finally decreases orbital moment contributions to both the magnetization and the MCA, respectively. This interplay of triagonal CF and SOC effects is further shown from the detailed quantitative analysis of the field-dependent magnetization in different orientations of CCO and ${\mathrm{Ca}}_3{\mathrm{Co}}_{1.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_6$ (CCFO) SCs at ambient pressure by employing a simple classical model and second-order perturbative analysis of SOC. The complete quenching of the orbital moment of ${\mathrm{Fe}}^{3+}$ ($S=5/2$) in CCFO weakens the MCA and also helps in deducing the SOC effect. Furthermore, the estimated anisotropic constants using density functional theory very well capture the Ising magnetism in CCO and deviation from it in CCFO compared to that of classical results.

The dynamics and interaction of different electronic phases near the metal-to-insulator transition of the phase-separated ${\left({\mathrm{La}}_{0.5}{\mathrm{Pr}}_{0.5}\right)}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_3$ (LPCMO) thin film grown on NGO substrate was studied using the first-order reversal curves (FORC) diagram method for electric transport measurements. The in-plane angle-dependent remanence and coercivity field in the region of the ferromagnet metallic phase was measured using the macroscopic magnetization technique. These measurements suggest an in-plane uniaxial magnetic anisotropy for the film with a uniaxial anisotropic constant (Ku) of $\sim 1.2\times {10}^6\mathrm{erg}/\mathrm{c}{\mathrm{m}}^3$ at 20 K. The angle dependence of the coercivity is best described by 1/cosθ dependence indicating that the magnetization reversal occurs mainly through the depinning of the domain wall, a signature of nucleation and propagation mechanism. The correlation of FORC measurements, resistance relaxation, and macroscopic magnetic measurements indicate a fast reversal of electronic and magnetic phases towards the denser phase region and strong interaction of different phases for the LPCMO system.

Muon spin rotation/relaxation ($\mu \mathrm{SR}$) and polar Kerr effect measurements provide evidence for a time-reversal symmetry breaking (TRSB) superconducting state in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. However, the absence of a cusp in the superconducting transition temperature ($T_{\mathrm{c}}$) vs stress and the absence of a resolvable specific heat anomaly at TRSB transition temperature ($T_{\mathrm{TRSB}}$) under uniaxial stress challenge a hypothesis of TRSB superconductivity. Recent $\mu \mathrm{SR}$ studies under pressure and with disorder indicate that the splitting between $T_{\mathrm{c}}$ and $T_{\mathrm{TRSB}}$ occurs only when the structural tetragonal symmetry is broken. To further test such behavior, we measured $T_{\text{c}}$ through susceptibility measurements and $T_{\text{TRSB}}$ through $\mu \mathrm{SR}$, under uniaxial stress applied along a $\langle 110\rangle$ lattice direction. We have obtained preliminary evidence for suppression of $T_{\text{TRSB}}$ below $T_{\text{c}}$, at a rate much higher than the suppression rate of $T_{\text{c}}$.

The short time (large energy) behavior of the Sachdev-Ye-Kitaev model (SYK) is one of the main reasons for the growing interest garnered by this model. True chaotic behavior sets in at the Thouless time, which can be extracted from the energy spectrum. In order to do so, it is necessary to unfold the spectrum, i.e., to filter out global tendencies. Using a simple ensemble average for unfolding results in a parametically low estimation of the Thouless energy. By examining the behavior of the spectrum as the distribution of the matrix elements is changed into a log-normal distribution, it is shown that the sample-to-sample level spacing variance determines this estimation of the Thouless energy. Using the singular value decomposition method, which filters out these global sample-to-sample fluctuations, the Thouless energy becomes parametrically much larger, essentially of the order of the band width. It is shown that the SYK model is non-self-averaging even in the thermodynamic limit which must be taken into account in considering its short time properties.

Short-range (SR) magnetic orders such as magnetic glass orders or fluctuations in a quantum system usually host exotic states or critical behaviors. Like the long-range (LR) magnetic orders, SR magnetic orders can also break time-reversal symmetry and drive the nonzero Berry curvature leading to novel transport properties. In this work, we report that in $\mathrm{Eu}{\mathrm{Zn}}_2{\mathrm{As}}_2$ compound, besides the LR $A$-type antiferromagnetic (AF) order, the SR magnetic order is observed in a wide temperature region. Magnetization measurements and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM) correlations for this SR magnetic order which results in an obvious anomalous Hall effect above the AF transition. Moreover the ESR results reveal that this FM SR order coexists with LR AF order exhibiting anisotropic magnetic correlations below the AF transition. The interactions of LR and SR magnetism evolving with temperature and field can host nonzero spin chirality and berry curvature leading to additional topological Hall contribution even in a centrosymmetric simple AF system. Our results indicate that $\mathrm{Eu}{\mathrm{Zn}}_2{\mathrm{As}}_2$ is a fertile platform to investigate exotic magnetic and electronic states.

Characteristics of topological semimetals such as a nonsaturating magnetoresistance (MR), a field-induced metal to semiconducting crossover and a robust resistivity plateau are observed under a magnetic field in type-I ${\mathrm{RbBi}}_2$ bulk superconductor with $T_{\mathrm{c}}=4.15$ K. The MR exhibits a notable 3500% increase at 2 K and 9 T and the resistivity follows a power law temperature dependence, while the MR $\propto H^{1.26}$, indicating weak carrier compensation. First principles calculations provided insights into the dynamical stability of the cubic structure at 0 K. Both hole and electron pockets are observed at the Fermi surface. The electron-phonon interaction constant indicates weak coupling strength ($<1$) that leads to a maximum predicted $T_{\mathrm{c}}$ of 2.852 K. Just below the Fermi level, ${\mathrm{E}}_F$, the electronic band structure consists of linear band crossings at the $X$ points in the Brillouin zone (BZ) corresponding to massless, symmetry-protected Dirac fermions.

The sliding ferroelectricity is engineered by artificially stacking the nonpolar two-dimensional (2D) materials, which greatly broadens the 2D ferroelectrics from very few candidate materials to a large family of 2D materials. However, the electric polarizations are generally small due to the weak van der Waals interlayer interaction. The search for 2D sliding ferroelectrics with large polarization presents an ongoing challenge. Here we systematically investigate the sliding ferroelectricity in the bilayer honeycomb structures of $\mathrm{B}X$ $(X=\mathrm{P}, \mathrm{As}, \mathrm{Sb})$, $Y\mathrm{N}$ $(Y=\mathrm{Al}, \mathrm{Ga}, \mathrm{In})$, and $Z\mathrm{C}$ $(Z=\mathrm{Si}, \mathrm{Ge}, \mathrm{Sn})$ based on first-principles calculations. It is shown that the electric polarization decreases with the increase of the interlayer distance, and increases with the difference in electronegativity of the two constituent elements. Such dependence is further corroborated by a simple model. It is interesting to see that GeC can be an ideal sliding ferroelectric material with high polarization and energetically favorable polar stacking. Our results reveal the key factors in determining the electric polarization, which could facilitate the search and design of 2D sliding ferroelectrics with large out-of-plane polarization.

We theoretically investigate a practically realizable Floquet topological superconductor model based on a one-dimensional Rashba nanowire and proximity-induced $s$-wave superconductivity in the presence of a Zeeman field. The driven system hosts regular 0-Majorana end modes and anomalous $\pi$-Majorana end modes (MEMs). By tuning the chemical potential and the frequency of the drive, we illustrate the generation of multiple MEMs in our theoretical setup. We utilize the chiral symmetry operator to topologically characterize these MEMs via a dynamical winding number constructed out of the periodized evolution operator. Interestingly, the robustness of the 0- and $\pi$-MEMs is established in the presence of on-site time-independent random disorder potential. We employ the twisted boundary condition to define the dynamical topological invariant for this translational-symmetry broken system. The interplay between the Floquet driving and the weak disorder can stabilize the MEMs, giving rise to a quantized value of the dynamical winding number for a finite range of drive parameters. This observation might be experimentally helpful in scrutinizing the topological nature of the Floquet MEMs. We showcase another driving protocol, namely, a periodic kick in the chemical potential, to study the generation of Floquet MEMs in our setup. Our work paves a realistic way to engineer multiple MEMs in a driven system.

We study the effects of thermal fluctuations and pinned boundaries in graphene membranes by using a phase-field crystal model with out-of-plane deformations. For sufficiently long times, the linear diffusive behavior of height fluctuations in systems with free boundaries becomes a saturation regime, while at intermediate times the behavior is still subdiffusive as observed experimentally. Under compression, we find mirror buckling fluctuations where the average height changes from above to below the pinned boundaries, with the average time between fluctuations diverging below a critical temperature corresponding to a thermally induced buckling transition. Near the transition, we find a nonlinear height response in agreement with recent renormalization-group calculations and observed in experiments on graphene membranes under an external transverse force with clamped boundaries.

A systematic analysis of the electronic and thermal properties of two semiconducting monolayers, SnSi and SnGe, is conducted through the lens of density functional theory. Unlike centrosymmetric graphene, these two monolayers are noncentrosymmetric and buckled in the structure; however, their band dispersion resembles that of graphene with a finite small band gap occurring at the $K$ point of the Brillouin zone. Unlike transition metal dichalcogenide (TMDC) monolayers, the band edges in the studied semiconducting monolayers are devoid of $d$ orbitals and contain $s$ and $p$ orbitals, and thus, the valley spin splitting occurring in these semiconductors is a nontrivial topological effect originating from broken inversion symmetry in the crystal structure, as observed earlier in bilayer graphene or graphene-based van der Waals heterostructures. The electronic properties are found to be tunable via external perturbations like an electric field and biaxial strain. These monolayers are highly flexible, as indicated by the small value of Young's modulus, $<50\mathrm{N}/\mathrm{m}$. The charge carrier mobility is calculated within the Boltzmann transport equation and found to be $\sim 1000\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-}1{\mathrm{s}}^{-1}$. The phonon dynamics study indicates a very low value of lattice thermal conductivity at room temperature (i.e., ${\kappa }_l<1.5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$), which arises from the domination of Umklapp scattering, small group velocity, and low Debye temperature. Such a low value of ${\kappa }_l$ will facilitate better thermal control than TMDCs or graphene-based devices. In this paper, we indicate that the inherent properties of SnSi and SnGe monolayers, such as valley contrasting properties, high charge carrier mobility, low lattice thermal conductivity, and mechanical flexibility, surpass that of well-known TMDCs (${\mathrm{MoS}}_2, {\mathrm{WS}}_2$) and boron pnictides (BP, BAs, BSb), thereby motivating their synthesis.

Three-dimensional higher-order topological insulators can have topologically protected chiral modes propagating on their hinges. Hinges with two copropagating chiral modes can serve as a “beam splitter” between hinges with only a single chiral mode. Here we show how such a crystal, with Ohmic contacts attached to its hinges, can be used to realize a Mach-Zehnder interferometer. We present concrete calculations for a lattice model of a first-order topological insulator in a magnetic field, which, for a suitable choice of parameters, is an extrinsic second-order topological insulator with the required configuration of chiral hinge modes.

The valley-Hall effect provides topological protection to a broad class of defects in valley-Hall photonic topological metamaterials. Unveiling precisely how such protection is achieved and its implications in practical implementations is paramount to move from fundamental science to applications. To this end, we investigate a honeycomb valley-Hall topological metamaterial and monitor the evolution of the topological valley-Hall edge states and higher-order corner states under different perturbation $\delta R$. The evolutions of the edge states of the armchair and zigzag interfaces are demonstrated, respectively. By adjusting the geometric parameters and introducing disturbances to break the inversion symmetry, we achieve the edge states with different modes including the conventional crossed edge state and the specific gapped edge state. It is found that the edge states of topological valley kinking will gradually separate with the increase of $\delta R$, and finally a complete gap between the edge states appears. The gap has rarely been reported previously in topological materials fabricated by printed circuit board technology. In addition, the higher-order topological corner states can also be observed in the proposed topological metamaterial. The higher-order topological phase is theoretically characterized by nontrivial bulk polarization and the Wannier centers. Our results show that the corner state localization becomes stronger with the increase of $\delta R$. It is expected that our results will provide a platform for the realization of optical topological insulators.

Purely ballistic transport is a rare feature even for integrable models. By numerically studying the Heisenberg chain with the power-law exchange, $J\propto 1/r^{\alpha }$, where $r$ is a distance, we show that for spin anisotropy $\mathrm{\Delta }\simeq exp(-\alpha +2)$ the system exhibits a quasiballistic spin transport and the presence of fermionic excitation, which do not decay up to extremely long times $\sim {10}^3/J$. This conclusion is reached on the basis of the dynamics of spin domains, the dynamical spin conductivity, inspection of the matrix elements of the spin-current operator, and analysis of most conserved operators. Our results smoothly connect two models in which fully ballistic transport is present: free particles with nearest-neighbor hopping and the isotropic Haldane-Shastry model.

The intrinsic ferromagnetic (FM) axion insulators and Weyl semimetals (WSMs) with only a single pair of Weyl points have drawn intensive attention but so far remain rare and elusive in real materials. Here, we propose a new class of $\mathrm{Mn}{X}_2{B}_2{T}_6$-B ($X$ = Ge, Sn, or Pb; $B$ = Sb or Bi; $T$ = Se or Te) family that is the stable structural form of this system. We find that the $\mathrm{Mn}{X}_2{B}_2{T}_6$-B family has not only the intrinsic FM axion insulators ${\mathrm{MnGe}}_2{\mathrm{Bi}}_2{\mathrm{Te}}_6$-B, ${\mathrm{MnSn}}_2{\mathrm{Bi}}_2{\mathrm{Te}}_6$-B, and ${\mathrm{MnPb}}_2{\mathrm{Bi}}_2{\mathrm{Te}}_6$-B, but also the intrinsic WSM ${\mathrm{MnSn}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_6$-B with only a single pair of Weyl points. Thus, the $\mathrm{Mn}{X}_2{B}_2{T}_6$-B family can provide an ideal platform to explore the exotic topological magnetoelectric effect and the intrinsic properties related to Weyl points.