We theoretically show that in the presence of conventional or higher order Van Hove singularities (VHS), the bare finite momentum pairing, also known as the pair density wave (PDW), susceptibility can be promoted to the same order of the most divergent bare BCS susceptibility through a valley-contrasting flux $3\varphi$ in each triangular plaquette at $\varphi =\pi /3$ and $\pi /6$ in moiré systems. This makes the PDW order a possible leading instability for an electronic system with repulsive interactions. We confirm that it indeed wins over all other instabilities and becomes the ground state under certain conditions through the renormalization group calculation and a flux insertion argument. Moreover, we also find that a topological nontrivial loop current order becomes the leading instability if the Fermi surface with conventional VHS is perfectly nested at $\varphi =\pi /3$. Similar to the Haldane model, this loop current state has the quantum anomalous Hall effect. If we dope this loop current state or introduce a finite next-nearest-neighbor hopping $t^{\prime }$, the chiral $d$-wave PDW becomes the dominant instability. Experimentally, the flux can be effectively tuned by an out-of-plane electric field in moiré systems based on graphene and transition metal dichalcogenides.

We clarify the ground-state phase diagram of the half-filled square-lattice Hubbard model with Rashba spin-orbit coupling (SOC) characterized by the spin-split energy bands due to broken inversion symmetry. Although the Rashba metals and insulating magnets have been studied well, the intermediate interaction strength of the system remained elusive due to the lack of appropriate theoretical tools to unbiasedly describe the large-scale magnetic structures. We complementarily apply four different methods (sine-square deformed mean-field theory, random phase approximation, Luttinger-Tisza method, and density matrix embedding theory) and succeed in capturing the incommensurate spin-density-wave (SDW) phases with very long spatial periods which were previously overlooked. The transition to the SDW phases from the metallic phase is driven by an unprecedented instability that nests the two parts of the Fermi surface carrying opposite spins. For large SOC, the spiral, stipe, and vortex phases are obtained, when the four Dirac points exist near the Fermi level and their whole linear dispersions nest by a wavelength $\pi$, opening a band gap. These two types of transition provide Fermiology that distinguishes the antisymmetric SOC systems, generating a variety of magnetic phases that start from the relatively weak correlation regime and continue to the strongly interacting limit.

Both multiple steady states and dark states have potential applications in the quantum information processing in the presence of dissipation. Here, we propose to implement multiple steady states and dark states in a double quantum dot (DQD) system using quantum reservoir engineering. By coupling the DQD to shared reservoirs, multiple steady states of both four- and two-fold degeneracy can be achieved for specific parameters. It is proved that the occurrence of such multiple steady states is attributed to the strong symmetry of the Lindblad master equation. The multiple steady states can be well revealed by the occupation number of the DQD, which exhibits a discontinuity at the strong-symmetric points and changes drastically in the vicinities of these points. In the regime of unique steady state, the system can be stabilized to a pure state, dubbed dark state, with intact coherence in spite of the dissipation. Our work shows that a variety of novel steady states can be implemented in the DQD system, which paves the way for engineering multiple steady states and dark states in the DQD system.

We investigate the strong coupling between excitons and quasibound states in the continuum (BICs) resonance in a bulk ${\mathrm{WS}}_2$ metasurface. Here, we employ bulk ${\mathrm{WS}}_2$ to construct an ultrathin nanodisk metasurface, supporting the symmetry-protected magnetic dipole quasi-BIC resonance, which can self-hybridize with the excitons and lead to a strong light-matter interaction enhancement within the structure without the necessity for an external cavity. This strong coupling can be characterized by the considerable Rabi splitting of 159 meV and the clearly anticrossing behavior appearing in the absorption spectrum. Furthermore, we analyze such light-matter coupling by constructing a Hamiltonian model including the surplus excitons and tune the interaction from weak- to strong-coupling regimes via the tunability radiation loss of the quasi-BIC resonance. Our results have great potential for manipulating the exciton-polaritons at room temperature and provide a promising prospect for photonic devices that exploit strong coupling in applications.

In contrast with extensive investigations on the translation of domain walls (DWs) in antiferromagnetic (AFM) materials, the precessional motion of an AFM DW is seldom concerned partly because of the lack of an effective driving method. In this Letter, we show that under an alternating spin-polarized current with polarization along the AFM anisotropy axis, an AFM DW can be excited to precess. Especially, chaotic precession occurs at a moderate interfacial Dzyaloshinskii-Moriya interaction (DMI), which contributes to a nonlinear term in the dynamic equation of DW precession. Crisis-induced intermittent chaos appears when the current density is higher than a critical value. This Letter not only paves a way to unravel the rich dynamics of a current-induced AFM texture but also provides guidelines for developing ultrafast spintronic devices to exploit the nonlinear chaotic magnetization dynamics with promising applications.

The discovery of superconductors with higher superconducting transition temperatures ($T_{\mathrm{c}}$'s) at ambient physical conditions is a perpetual drive in fundamental studies and for practical applications. Here we conceptualize two generic rules for achieving this goal surrounding metal hydride superconductors. Rule 1: the metal skeletons should be composed of elements with an effective valency of 3 for efficient electron donation to hydrogen. Rule 2: the fractional occupancy of the metal ions should be $\sim 0.4$ for maximal chemical squeezing on hydrogen. Guided by these rules, and based on first-principles approaches, we predict a collection of new hydride superconductors, including the representative examples of ${\mathrm{CaHfH}}_{12}$, with $T_{\mathrm{c}}$ of $\sim 360$ K at 300 GPa, and ${\mathrm{CaZrH}}_{12}$, with $T_{\mathrm{c}}$ of $\sim 290$ K at 200 GPa. These findings are expected to be instrumental in predictive discoveries of new high-$T_{\mathrm{c}}$ hydride superconductors at lower pressures.

By using the tensor-network state algorithm, we study a spin-orbital model with $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)\times \mathrm{U}\left(1\right)$ symmetry on the triangular lattice. This model was proposed to describe some triangular $d^1$ materials and was argued to host a spin-orbital liquid ground state. In our work the trial wave function of its ground state is approximated by an infinite projected entangled simplex state and optimized by the imaginary-time evolution. Contrary to the previous conjecture, we find that the two SU(2) symmetries are broken, resulting in a stripe spin-orbital order with the same magnitude $m=0.085\left(10\right)$. This value is about half of that in the spin-1/2 triangular Heisenberg antiferromagnet. Our result demonstrates that although the long-sought spin-orbital liquid is absent in this model the spin-orbital order is significantly reduced due to the enhanced quantum fluctuation. This suggests that high-symmetry spin-orbital models are promising in searching for exotic states of matter in condensed-matter physics.

We identify a sizable nonlinear Hall effect of spin-3/2 heavy holes in zincblende nanostructures, driven by a quadrupole interaction with the electric field formerly believed to be negligible. The interaction is enabled by $T_d$-symmetry, reflects inversion breaking, and in two dimensions results in an electric-field correction to the in-plane $g$ factor. The effect can be observed in state-of-the-art heterostructures, either via magnetic doping or by using a vector magnet, where even for small perpendicular magnetic fields it is comparable in magnitude to topological materials.

In the present Letter, we have used magnetocapacitance and magnetoresistance measurements to investigate nonequilibrium phenomena in a bilayer electron system based on GaAs/AlGaAs heterostructures. The magnetic field ramping drives the bilayer electron system out of equilibrium, leading to magnetoresistance hysteresis and spikes. Unlike magnetoresistance, magnetocapacitance results intriguingly show hysteresis even when both layers are in the quantum Hall state. The hysteresis is accompanied by interlayer charge transfer, but the disequilibrium is not limited to interlayer imbalance. Results show that the edge-bulk imbalance can be the initial ground for the appearance of hysteresis. In addition, the nonequilibrium states are observed in which the total, rather than individual, layer densities determine the magnetic field and gate voltage dependencies.

Topological defects in solid-state materials are crystallographic imperfections that local perturbations cannot remove. Owing to their nontrivial real-space topology, topological defects such as dislocations and disclinations could trap anomalous states associated with nontrivial momentum-space topology. The real-space topology of dislocations and disclinations can be characterized by the Burgers vector $\mathbf{B}$, which is usually a fixed fraction and integer of the lattice constant in solid-state materials. Here we show that in a dielectric photonic crystal—an artificial crystalline structure—it is possible to tune $\mathbf{B}$ continuously as a function of the dielectric constant of dislocations. Through this unprecedented tunability of $\mathbf{B}$, we achieve proper controls of topological interfacial states, i.e., reversal of their helicities. Based on this fact, we propose a topological optical switch controlled by the dielectric constant of the tunable dislocation. Our results shed light on the interplay of real and reciprocal space topologies and offer a scheme to implement scalable and tunable robust topological waveguides in dielectric photonic crystals.

Although [100] lithium flouride (LiF) is the most widely used optical window material in dynamic compression experiments, its high stress ($>100\mathrm{GPa}$) shock compression response, including melting, is not well understood. To address this need, we measured wave profiles in plate impact experiments to determine the Hugoniot states and longitudinal sound speeds in [100] LiF crystals shock compressed to 231 GPa. The measured peak states are fitted well by a linear shock velocity–particle velocity relation, providing an accurate determination of the LiF Hugoniot curve to significantly higher stresses than previous experiments. The longitudinal sound speeds show a near linear increase with density compression to 182 GPa. Between 182 GPa and 195 GPa, the sound speed and the longitudinal modulus decrease abruptly, due to shock-induced melting. The increasing sound speeds and moduli at higher stresses suggest that shock compressed LiF is fully liquid at 195 GPa and above, allowing determination of the Grüneisen parameter for liquid LiF. The melt stress determined here differs from that predicted by current multiphase equations of state for LiF. Our results provide important insight into the high stress solid and liquid states of shock compressed LiF and point to the need for an improved multiphase equation of state at high pressures and high temperatures.

Recently discovered higher-order states extensively enrich the study of topological phases, allowing one to manipulate wave propagating or localizing in more than one dimension lower than the bulk. To date, vast higher-order topological phases have been demonstrated in photonics, acoustics, mechanics, and electronics; however, these are usually in magnetic-free scenarios. Here, we report our realization of magnetic corner states in a two-dimensional honeycomb lattice gyromagnetic photonic crystal. By simultaneously breaking both time-reversal and parity symmetries with one-sublattice magnetic bias, we elaborately gap the native gapless chiral edge states of the quantum-Hall phase. In the complete band gaps, we experimentally observe a pair of unconventional corner states originating from the hybridization of two Wannier centers to shape symmetrical and antisymmetrical modes. Furthermore, we can switch on (off) the corner field localizations solely by adding (removing) the magnetic fields of the corner sites without changing other configurations.

We investigate localization and topological properties of a dimerized Kitaev chain with $p$-wave superconducting correlations and a quasiperiodically modulated chemical potential. With regard to the localization studies, we demonstrate the existence of distinct phases, such as, the extended phase, the critical (intermediate) phase, and the localized phase that arise due to the competition between the dimerization and the on-site quasiperiodic potential. Most interestingly, the critical phase comprises of two different anomalous mobility edges that are found to exist between the extended to the localized phase, and between the critical (multifractal) and localized phases. We perform our analysis employing the inverse and the normalized participation ratios, fractal dimension, and the level spacing. Subsequently, a finite-size analysis is done to provide support of our findings. Furthermore, we study the topological properties of the zero-energy edge modes via computing the real-space winding number and number of the Majorana zero modes present in the system. We specifically illustrate that our model exhibits a phase transition from a topologically trivial to a nontrivial phase (topological Anderson phase) beyond a critical dimerization strength under the influence of the quasiperiodic potential strength. Finally, in presence of a large potential, we demonstrate that the system undergoes yet another transition from the topologically nontrivial to an Anderson localized phase. Thus, we believe that our results will aid exploration of fundamentally different physics pertaining to the critical and the topological Anderson phases.

We analyze the effect of the tilt on the transverse thermoelectric coefficient of Weyl semimetals in the conformal limit, i.e., zero temperature and zero chemical potential. Using the Kubo formalism, we find a nonmonotonic behavior of the thermoelectric conductivity as a function of the tilt perpendicular to the magnetic field, and a linear behavior when the tilt is aligned to the magnetic field. An “axial Nernst” current (chiral currents counter propagating perpendicularly to the magnetic field and the temperature gradient) is generated in inversion symmetric Weyl materials when the tilt vector has a projection in the direction of the magnetic field. This analysis will help in the design and interpretation of thermoelectric transport experiments in recently discovered topological quantum materials.

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities for switching solids between distinctly-different crystalline, electronic, and magnetic states and thus modify their functional properties in a significant way. In this paper, we report on the laser-induced spin reorientation and Verwey phase transitions in a single crystalline ferrimagnetic magnetite ${\mathrm{Fe}}_3{\mathrm{O}}_4$. Using femtosecond optical and magneto-optical pump-probe techniques, we define the range of the initial sample temperatures and laser fluences when partial or complete photo-induced phase transitions occur from a monoclinic insulating to a cubic metallic state with concomitant switching of magnetic anisotropy from the uniaxial to the cubic one. We thus reveal a connection between these phase transitions when driven by femtosecond laser pulses. Using transient linear and quadratic magneto-optical effects, we examine magnetization dynamics launched the switching of the magnetic anisotropy axis. We unveil the presence of the domains undergoing the laser-induced phase transitions even below the established threshold fluence for the transitions, as well as when the material is initially in the cubic phase. This is the manifestation of the first order of these both laser-induced phase transitions beyond the range of thermodynamic equilibrium.

The design of high-temperature ferrimagnetic materials is highly demanded for next-generation functional spintronic devices. Here, we propose that the combination of nonmetallic structural units and magnetic atoms is an effective way to achieve high-temperature magnetism in two-dimensional (2D) materials. The predicted $\mathrm{Fe}{\mathrm{P}}_4$ monolayer, consisting of quasisquare ${\mathrm{P}}_4$ units, shows intrinsic half-metal ferrimagnetism above room temperature. Each Fe atom is coordinated with four P atoms associated with the surrounding four quasisquare ${\mathrm{P}}_4$ units. First-principles calculations suggest that the $\mathrm{Fe}{\mathrm{P}}_4$ monolayer presents a Curie temperature of 460 K. More interestingly, the itinerant electrons and the unique quasisquare ${\mathrm{P}}_4$ units act as intermediaries and play an important role in promoting the Ruderman-Kittel-Kasuya-Yosida and superexchange interactions, respectively, which induces a robust ferrimagnetism. Our findings not only shed light on the promising future of 2D magnetic materials, but also are of interest for high-temperature spintronic applications.

Recent experiments have pointed to chiral $p$-wave-like superconductivity in epitaxial Bi/Ni bilayers that are spontaneously time-reversal symmetry breaking (TRSB), making it a promising platform for exploring physics useful for topologically protected quantum computing. Quite intriguingly, evidence has emerged that, in nonepitaxial Bi/Ni bilayers, superconductivity arises due to the formation of $\mathrm{Ni}{\mathrm{Bi}}_3$, which has been reported to host coexisting ferromagnetic and superconducting orders at the surface. We perform high-resolution surface magneto-optic Kerr effect measurements using a Sagnac interferometer on single-crystal $\mathrm{Ni}{\mathrm{Bi}}_3$ and find no sign of any spontaneous Kerr signal except for contributions from trapped vortices. This strongly indicates the absence of TRSB in $\mathrm{Ni}{\mathrm{Bi}}_3$, whether due to TRSB in the superconducting state or any coexisting ferromagnetism, and we conclude that the superconductivity found in nonepitaxial Bi/Ni is distinctively different from that in epitaxial Bi/Ni.

We theoretically study the electric pulse-driven nonlinear response of interacting bosons loaded in an optical lattice in the presence of an incommensurate superlattice potential. In the noninteracting limit $(U=0)$, the response of the localized phase differs significantly than the response of the delocalized phases. In particular, we show that the particle current contains only odd harmonics in the delocalized phase in contrast to the localized phase where both even and odd harmonics exist. The relative magnitudes of these even and odd harmonics and the contrast of the peaks can be tuned by varying frequency and the number of cycles of the applied pulse, respectively. In the presence of repulsive interactions, the amplitudes of the even and odd harmonics further depend on the relative strengths of the interaction $U$ and the disorder potential $V_0$. We illustrate that the disorder and interaction-induced phases can be distinguished through the particle current. Finally, we discuss the dynamics of field-induced excitation responsible for exhibiting higher harmonics in the current spectrum.

We calculate the Ruderman-Kittel-Kasuya-Yosida interaction between impurity spins, localized at the surface of an imperfect topological insulator (TI). Namely, we consider the warping and tilting of a TI Dirac cone. We show that the warping and tilting addition to the initial Rashba spin-orbit interaction (SOI) yields a highly anisotropic response to the localized spin rotation. Also, the Friedel oscillation strength of such an imperfect TI depends on the direction in its plane. Latter dependence, parametrized by Lissajous curves of spin-response components, can serve as a “fingerprint” of the initial Dirac cone distortion in the TI. The ensuing unusual dynamics is due to the interplay of SOI, warping and tilting of the initial Dirac cone, and the resulting indirect exchange between localized impurities. Variation of the warping and tilting strengths can be used to manipulate the impurity spin reversal, which is important for technological applications.