A reference lattice, away from which elastic distortions induced by the spin texturing of two-dimensional (2D) magnets take hold, is motivated from a picture of pairwise Biot-Savart interactions among identical solenoids that either elongate or compress a (“zero-current”) spring lattice. Applied to a paradigmatic ${\mathrm{CrSiTe}}_3$ monolayer, the reference is given by the average between the atomic positions of ferromagnetic (FM) and Néel antiferromagnetic (AFM) lattices; such an atomic disposition permits understanding structural distortions and elastic energies due to magnetism readily. Furthermore, the anisotropic speed of sound in the magnetic ground state explains an observed anisotropy of vibrational frequencies on similar magnets. Elastic stiffness constants are reported, too. Magnetic energies in four Ising structural configurations were calculated and the strain needed for those 2D magnets to undergo an AFM to FM quantum phase transition was determined as well.

A recent observation of the in-plane anomalous Hall effect in the magnetic Weyl semimetal ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$ has drawn attention to out-of-plane orbital magnetization induced by an in-plane field component. Here, we study ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$, a sister compound of ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$, to demonstrate sensitive changes of the in-plane anomalous Hall effect on the band modulation. The Hall resistivity measured with rotating the magnetic field within the (001) principal plane of ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$ films exhibits a clear threefold component corresponding to the in-plane anomalous Hall effect, which is distinct from the twofold component of the planar Hall effect. The in-plane anomalous Hall effect of ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$ is highly contrasting to ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$, especially in terms of its opposite sign and field dependence, which can be explained by model calculations with different band inversion parameters. Our results pave the way for systematically controlling the in-plane anomalous Hall effect and orbital magnetization through elaborate band engineering.

We investigate the localization, topological properties, and non-Hermitian skin effect in the non-Hermitian Aubry-André-Harper model, incorporating complex quasiperiodic potential and both unmodulated and modulated nonreciprocal hopping. Using Avila's global theory, we calculate the Lyapunov exponent to quantify the localization of eigenstates. The phase diagram of the system, after rescaling the imaginary phase, matches that of the Hermitian counterpart. Loops in the complex spectrum appear only in the localized phase, and we demonstrate that topological transitions coincide with localization transitions. For nonreciprocal hopping, the phase-transition lines obtained by analyzing the asymmetric localization behavior in the localized phase using similarity transformations are consistent with Avila's predictions. Under periodic boundary conditions, the complex spectrum always contains loops, and the topological phase transition aligns with the localization transition. For unmodulated nonreciprocal hopping, the extended phase transitions into a skin phase under open boundary conditions, while the critical phase remains unaffected. In contrast, modulated nonreciprocal hopping drives both the extended and critical phases into skin phases.

The magnetic ground state of geometrically frustrated antiferromagnets has attracted great research interest due to the possibility to realize novel quantum magnetic states such as a quantum spin liquid. Here we present a comprehensive magnetic characterization of ${\mathrm{DyTa}}_7{\mathrm{O}}_{19}$ with an ideal two-dimensional triangular lattice. ${\mathrm{DyTa}}_7{\mathrm{O}}_{19}$ exhibits $c$-axis single-ion magnetic anisotropy. Although long-range magnetic order is not observed down to 100 mK under zero field, by applying a small magnetic field ($\sim 0.1$ T), a magnetically ordered state with net magnetization of $M_s/3$ below $T_m=0.14\mathrm{K}$ is identified ($M_s$ denotes the saturated magnetization). We argue that this state is an up-up-down magnetic structure phase driven by the dipole-dipole interactions between Ising-like spins of ${\mathrm{Dy}}^{3+}$ in a two-dimensional triangular lattice, since its ordering temperature and temperature-field phase diagram can be well explained by the theoretical calculations based on dipolar interactions. ${\mathrm{DyTa}}_7{\mathrm{O}}_{19}$ could be viewed as a rare material platform that realizes pure Ising-like dipolar interaction in a geometrically frustrated lattice.

The first-order magnetic phase transition (MPT) usually happens with a very wide magnetic field span of about tens of thousands Oersteds which hinders its applications. In this work, we induce a domino-like MPT via introducing a bias voltage in FeRh thin film and thus realize a large narrowing of transition magnetic field span from $6\times {10}^4$ Oe to lower than $2\times {10}^3$ Oe at room temperature. Meanwhile, nonvolatile switchings with respect to the voltage pulses between pure magnetic phases of FeRh at room temperature can also be realized. The critical condition and phase diagram for domino-like MPTs are obtained in theory and our experiments support it well. Our works not only benefit the studies and applications of MPT-based devices but also are significant in the applications of the phase transition systems with resistance change.

Hydrogen in its metallic form is the most common material in our solar system, found under the extreme pressure and temperature conditions found in giant planets. Such conditions are inaccessible to experiments and, consequently, theoretical work has typically led experiments. Metallic hydrogen is also expected to exist in solid form at low temperatures and to have remarkable properties. It has been the subject of several controversial claims of synthesis. A curious feature is that solid metallic hydrogen is not expected to have a close-packed structure, even at extreme pressures. The predicted crystal structure has a packing fraction of only 0.44 compared with 0.74 for fcc. Alloying with other metallic elements can form compounds with atomic hydrogen and much reduced metallization pressure. Here we investigate the possible solid solubility of a representative range of elements (Be, B, Mg, S, Fe, La) in metallic atomic hydrogen near 500 GPa. We find that zero point energy is a highly significant feature in all cases. The metallic elements Be, Mg, Fe, and La have a well-defined clathrate-style first-neighbor shell at 300 K, while the nonmetallic B and S have more open arrangements. All the elements considered are soluble, in sites substituting for more than one hydrogen atom. The solid solubility of such a wide range of ambient bonding types—simple metals, covalent materials, transition metals, lanthanides—gives a strong indication that most elements will dissolve in solid metallic hydrogen. Atomic metallic hydrogen is far more aggressively corrosive than its molecular counterpart, which adds to the practical challenge for synthesis. Such doping raises the possibility of synthesizing $I{4}_1$/amd hydrogen at somewhat lower pressure.

Effects of the three-dimensional (3D) interplanar coupling on centrosymmetric skyrmion crystal (SkX) formation is investigated via extensive Monte Carlo simulations on the frustrated isotropic Heisenberg model on a stacked-triangular lattice in both cases of the ferromagnetic (F) and the antiferromagnetic (AF) nearest-neighbor interplanar coupling $J_{1c}$. The SkX phase is stabilized at finite fields and at finite temperatures for both F and AF $J_{1c}$, although it is destabilized by modestly weak AF $J_{1c}$. The magnetic phase diagram of the 3D short-range model is more or less similar to those of the 2D short-range model and of the 2D long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) model. We find that an intriguing phenomenon of replica-symmetry breaking, popular in glass physics and recently identified in the SkX phase of the 3D long-range RKKY model [K. Mitsumoto and H. Kawamura, Phys. Rev. B 104, 184432 (2021)], does not arise in the 3D short-range model, suggesting that the long-range nature of interaction might be necessary to realize the replica-symmetry breaking in a centrosymmetric SkX state.

Recently introduced magnetic materials called altermagnets (AM) feature zero net magnetization but a momentum-dependent magnetic exchange field, which can have intriguing implications when combined with superconductivity. In our work, we use the quasiclassical framework to study the effects of such a material on a conventional superconductor (S) in an AM/S bilayer. We discuss the superconducting phase diagram and heat capacity of AM/S while making a comparison with a ferromagnet-superconductor bilayer. Furthermore, we examine the density of states and analyze the system's response to an external magnetic field. We illustrate the anisotropy of spin susceptibility and magnetization of AM/S by considering an external field in the in-plane and out-of-plane directions, thereby facilitating the scope of experimental detection and characterization of an AM in an AM/S hybrid system.

Topological order is a promising basis for quantum error correction, a key milestone towards large-scale quantum computing. Floquet codes provide a dynamical scheme for this while also exhibiting Floquet-enriched topological order where anyons periodically undergo a measurement-induced automorphism that acts uniformly in space. We study disordered Floquet codes where automorphisms have a spatiotemporally heterogeneous distribution: the automorphisms “compete.” We characterize the effect of this competition, showing how key features of the purification dynamics of mixed code states can be inferred from anyon and automorphism properties for any Abelian topological order. This perspective can explain the preservation or measurement of logical information in a dynamic automorphism (DA) code when subjected to a noise model of missing measurements. We demonstrate this using a DA color code with perturbed measurement sequences. The framework of competing automorphisms captures essential features of Floquet codes and robustness to noise, and may elucidate key mechanisms involving topological order, automorphisms, and fault tolerance.

The third-order anomalous Hall effect (TOAHE) driven by Berry connection polarizability in Dirac materials offers a promising avenue for exploring quantum geometric phenomena. We investigate the role of impurity scattering on TOAHE using the semiclassical Boltzmann framework, via a comparison of the intrinsic contributions (stemming from the Berry connection polarizability) with the extrinsic contributions caused by the disorder. To validate our theoretical findings, we employ a generalized two-dimensional low-energy Dirac model to analytically assess the intrinsic and extrinsic contributions to the TOAHE. Our analysis reveals distinct disorder-mediated effects, including skew-scattering and side-jump contributions. We also elucidate their intriguing dependencies on Fermi-surface anisotropy and discuss opportunities for experimental exploration.

Rydberg states of excitons in ${\mathrm{Cu}}_2\mathrm{O}$ are known to interact strongly with other carriers in their surrounding such as other excitons, free charge carriers, and static charged impurities. In continuous-wave experiments, discriminating the individual processes is notoriously challenging. Here, we use a time-resolved two-color pump-probe setup and investigate the temporal evolution of Rydberg excitons with a resolution of 15 ns. The dynamic response of the Rydberg system to pump pulses with different energies is analyzed and the elementary processes that constitute the complex decay dynamics are compared among the different excitation scenarios. Our analysis reveals mainly four different timescales on which physical processes occur.

Magnetotransport phenomena often provide critically important information about two-dimensional (2D) electron systems. For example, the independence of magnetophotoresistance of 2D electrons in best-quality quantum wells on the polarization helicity of incident radio-frequency radiation has been treated as a puzzling effect, which is important for characterization of these systems, but had no well-established explanation up to now. Here we develop a phenomenological model of dynamics of a highly correlated 2D electron fluid in moderate magnetic fields, in which shear viscosity and the memory effects in interparticle interaction are crucial. In this system, successive collisions of electrons joined in pairs (that is, the pair correlations in time) turn out to be as important as uncorrelated collisions of statistically independent electrons. The resulting photoresistance exhibits an irregular shape of magneto-oscillations, the absence of the dependence on the helicity of the circular polarization of radiation, and a giant peak near the doubled cyclotron frequency. All these effects were observed in experiments on best-quality GaAs quantum wells in moderate magnetic fields at low temperatures. Although the most general conditions of applicability of the developed phenomenological model are not fully clarified now, this coincidence can point out that 2D electrons in such systems form the highly correlated viscous fluid.

Materials with high thermal conductivity $\left(\mathrm{\Lambda }\right)$ are needed to conduct heat away from hot spots in high-power electronics and optoelectronic devices. Cubic boron arsenide (c-BAs) has a high thermal conductivity due to its special phonon dispersion relation. Previous experimental studies of c-BAs report a room-temperature thermal conductivity between 1000 and $1300\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. We synthesized high-purity isotopically enriched c-BAs single crystals with room-temperature thermal conductivity of $\approx 1500\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. Using time-domain thermoreflectance, we measured thermal conductivity and found a $1/T^2$ temperature dependence between 300 and 600 K–slightly stronger than predictions from state-of-the-art theoretical models. Brillouin and Raman scattering revealed minimal changes in phonon frequencies over the same temperature range, suggesting that the observed $1/T^2$ dependence is not caused by temperature-dependent changes in phonon dispersion. To probe defect densities in the BAs crystals we studied, we conducted transient reflectivity microscopy (TRM) measurements of absorption at sub-band-gap photon energies. We observe a correlation between TRM signal intensity and thermal conductivity. Notably, samples with thermal conductivity near $1500\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ still exhibited nonzero TRM signals, suggesting the presence of defects despite the high thermal conductivity.

Potential disorder in one dimension leads to Anderson localization of the entire spectrum. Upon sacrificing Hermiticity by adding nonreciprocal hopping, the non-Hermitian skin effect competes with localization. We find another route for delocalization, which involves imaginary potential disorder. While an entirely random potential generally still leads to localization, imposing minimal spatial structure to the disorder can protect delocalization: it endows the concomitant transfer matrix with an $\mathrm{SU}\left(2\right)$ structure whose compactness in turn translates into an infinite localization length. The fraction of delocalized states can be tuned by the choice of boundary conditions.

We examine the quantum phase transitions in a two-dimensional electron system hosted at a high-quality wide AlAs quantum well, with a particular focus on the integer filling factor of $\nu =2$ in the regime of the quantum Hall effect. The observed transitions are induced by the application of external strain to the structure and are manifested by a substantial change in the longitudinal resistance of the sample. The anisotropy of the $g$ factor permitted us to capture the spin resonances of electrons occupying the two in-plane valleys independently. An analysis of their amplitudes enabled us to attribute these transitions to the macroscopic modification of the valley “pseudospin” polarization, i.e., relative valley occupation, and to uncover the pseudospin evolution around these transitions.

Two-dimensional (2D) honeycomb lattices provide a versatile platform for realizing topologically nontrivial states. In this work, we uncover the coexistence and electrical tunability of quantum anomalous Hall (QAH) and quantum spin Hall (QSH) states in 2D honeycomb lattices characterized by non-Dirac band structures. Employing a tight-binding model, we demonstrate that $p_x$ and $p_y$ orbitals lead to quadratic non-Dirac band degeneracies at the $\mathrm{\Gamma }$ point and linear Dirac band degeneracies at the $\mathrm{K}$ and ${\mathrm{K}}^{\prime }$ points. The introduction of a magnetic exchange field and atomic spin-orbit coupling can induce distinct QAH and QSH gaps at separate energy levels within the same system. First-principles calculations validate these findings in a ferromagnetic monolayer of functionalized plumbene (${\mathrm{Pb}}_2\mathrm{BrO}$), predicting sizable QAH (175.4 meV) and QSH (187.8 meV) gaps. Notably, the Fermi energy of monolayer ${\mathrm{Pb}}_2\mathrm{BrO}$ resides in the QAH gap but can be electrically gated into the QSH gap, enabling reversible transitions between these two topologically nontrivial states. These results provide a theoretical foundation for the design of electrically tunable topological materials and establish 2D honeycomb lattices with non-Dirac bands as a promising platform for multifunctional quantum applications.

The advent of magnetic two-dimensional electron gases (2DEGs) at oxide interfaces has provided new opportunities in the field of spintronics. The enhancement of magnetism in 2DEGs at oxide interfaces continues to be a significant challenge, as exemplified by the relatively weak magnetism observed in the classical $\mathrm{LaAl}{\mathrm{O}}_3/\mathrm{SrTi}{\mathrm{O}}_3$ interface. Here, we present ferromagnetic (FM) 2DEGs at the interface fabricated between the FM insulator $\mathrm{EuTi}{\mathrm{O}}_3$ (ETO) and the strong spin-orbit coupled perovskite insulator $\mathrm{KTa}{\mathrm{O}}_3$ (KTO). With the combined effects of magnetic atom doping and magnetic proximity from ETO films, the coercive field of 2DEGs can be significantly enhanced. Magnetoresistance curve with a high coercive field of 1000 Oe has been observed, in conjunction with a temperature-dependent unambiguous hysteresis loop in the anomalous Hall effect. Furthermore, within the 2DEGs, we have identified a synergetic interplay between magnetic scattering and the weak antilocalization (WAL) effect on transport. This study provides fresh insights into the formation of FM 2DEGs at ETO/KTO interfaces, and introduce an innovative pathway for creating high-performance magnetic 2DEGs at oxide interfaces.

Choosing a basis set is the first step of a quantum chemistry calculation and it sets its maximum accuracy. This choice of orbitals is limited by strong technical constraints as one must be able to compute a large number of six-dimensional Coulomb integrals from these orbitals. Here we use tensor network techniques to construct representations of orbitals that essentially lift these technical constraints. We show that a large class of orbitals can be put into “tensorized” form including the Gaussian orbitals, Slater orbitals, linear combination thereof as well as new orbitals beyond the above. Our method provides a path for building more accurate and more compact basis sets beyond what has been accessible with previous technology. As an illustration, we construct optimized tensorized orbitals and obtain a 85% reduction of the error on the energy of the $H_2$ molecules with respect to a reference double-zeta calculation (cc-pvDz) of the same size.