The magnetic anisotropy of antiferromagnets plays a crucial role in stabilizing the magnetization of many spintronic devices. In noncollinear antiferromagnets such as IrMn, the symmetry and temperature dependence of the effective anisotropy are poorly understood. Theoretical calculations and experimental measurements of the effective anisotropy constant for IrMn differ by two orders of magnitude, while the symmetry has been inferred as uniaxial in contradiction to the assumed relationship between crystallographic symmetry and temperature dependence of the anisotropy from the Callen-Callen law. In this Rapid Communication, we determine the effective anisotropy energy surface of $\text{L}{1}_2$- ${\text{IrMn}}_3$ using an atomistic spin model and constrained Monte Carlo simulations. We find a unique cubiclike symmetry of the anisotropy not seen in ferromagnets and that metastable spin structures lower the overall energy barrier to a tenth of that estimated from simple geometrical considerations, removing the discrepancy between experiment and theory. The temperature scaling of the anisotropy energy barrier shows an exponent of 3.92, close to a uniaxial exponent of 3. Our results demonstrate the importance of noncollinear spin states on the thermal stability of antiferromagnets with consequences for the practical application of antiferromagnets in devices operating at elevated temperatures.

For the characterization of the dynamics in quantum many-body systems the question of how information spreads and becomes distributed over the constituent degrees of freedom is of fundamental interest. The delocalization of information under many-body dynamics has been dubbed scrambling, and out-of-time-order correlators were proposed to probe this behavior. In this work we investigate the time evolution of tripartite information as a natural operator-independent measure of scrambling, which quantifies to what extent the initially localized information can be recovered only by global measurements. Studying the dynamics of quantum lattice models with tunable integrability breaking, we demonstrate that in contrast to quadratic models generic interacting systems scramble information irrespective of the chosen partitioning of the Hilbert space, which justifies the characterization as a scrambler. Without interactions the dynamics of tripartite information in momentum space reveals unambiguously the absence of scrambling.

In this paper, we present novel experimental evidence for the odd-parity nematic superconductivity in high-quality single crystals of doped topological insulator ${\mathrm{Sr}}_x{\mathrm{Bi}}_2{\mathrm{Se}}_3$. The x-ray diffraction shows that the grown single crystals are either weakly stretched or compressed uniaxially in the basal plane along one of the crystal axis. We show that in the superconducting state, the upper critical magnetic field $H_{c2}$ has a twofold rotational symmetry and depends on the sign of the strain: in the stretched samples the maximum of $H_{c2}$ is achieved when the in-basal-plane magnetic field is transverse to the strain axis, while in the compressed samples this maximum is observed when the field is along the strain direction. This result is naturally explained within a framework of the odd-parity nematic superconductivity coupled to the strain. Magnetoresistance in the normal state is independent of the current direction and also has a twofold rotational symmetry that demonstrates the nematicity of the electronic system in the normal state.

We study the dynamics of charge-transfer insulators after a photoexcitation using the three-band Emery model which is relevant for the description of cuprate superconductors. We provide a detailed derivation of the nonequilibrium extension of the multiband $GW+\text{EDMFT}$ formalism and the corresponding downfolding procedure. The Peierls construction of the electron-light coupling is generalized to the multiband case resulting in a gauge invariant combination of the Peierls intraband acceleration and dipolar interband transitions. We use the formalism to study momentum-dependent (inverse) photoemission spectra and optical conductivities. The time-resolved spectral function shows a strong renormalization of the charge-transfer gap and a substantial broadening of some of the bands. While the upper Hubbard band exhibits a momentum-dependent broadening, an almost rigid band shift is observed for the ligand bands. The inverse photoemission spectrum reveals that the inclusion of nonlocal and interband charge fluctuations results in a very fast relaxation of the holes to the top of the Zhang-Rice singlet band. Consistent with the changes in the spectral function, the optical conductivity shows a renormalization of the charge-transfer gap, which is proportional to the photodoping. The details of the photoinduced changes strongly depend on the dipolar matrix elements, which calls for an ab initio determination of these parameters.

We propose a modified form of tensor renormalization-group algorithm for evaluating partition functions of classical statistical mechanical models on two-dimensional lattices. This algorithm coarse-grains only the rows and columns of the lattice adjacent to a single core tensor at each step, such that the lattice size shrinks linearly with the number of coarse-graining steps as opposed to shrinking exponentially as in the usual tensor renormalization group (TRG). However, the cost of this approach only scales as $O\left({\chi }^4\right)$ in terms of the bond dimension $\chi$, significantly cheaper than the $O\left({\chi }^6\right)$ cost scaling of TRG, whereas numerical benchmarking indicates that both approaches have comparable accuracy for the same bond dimension $\chi$. It follows that the algorithm can allow for more accurate investigation of classical models on modestly sized lattices than is possible with standard TRG.

We study the role of surface polaritons in the zero-temperature Casimir effect between two graphene layers that are described by the Dirac model. A parametric approach allows us to accurately calculate the dispersion relations of the relevant modes and to evaluate their contribution to the total Casimir energy. The resulting force features a change of sign from attractive to repulsive as the distance between the layers increases. Contrary to similar calculations that have been performed for metallic plates, our asymptotic analysis demonstrates that at small separations the polaritonic contribution becomes negligible relative to the total energy.

The effect of electron-electron interactions on the energy spectrum of surface electrons in a three-dimensional topological insulator is studied theoretically. The interaction includes both charge- and spin-dependent correlations. Using the Green's function method, we calculate the electron self-energy and determine the renormalized spin-orbit coupling strength. We find that the energy spectrum renormalized by spin-dependent electronic correlation turns nonlinear with respect to the wave vector $k$ measured from the perfect Dirac cone (in the absence of electron-electron interactions). We also discuss charge screening contributions from surface and bulk electrons.

Simultaneous control of structural and physical properties via applied electrical current poses a new, key research topic with both fundamental and technological significance. Studying the spin-orbit-coupled antiferromagnet ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$, and its derivative with 3% Mn doping to alleviate the violent first-order transition at 357 K, we find that a small applied electrical current couples to the lattice by significantly reducing its orthorhombic distortions and octahedral rotations, while concurrently diminishing the 125-K antiferromagnetic transition. Further increasing electrical current density above $0.15\mathrm{A}/\mathrm{c}{\mathrm{m}}^2$ induces a new nonequilibrium orbital state, with a transition signature at 80 K that features a simultaneous jump in both magnetization and electrical resistivity, sharply contrasting the current-free state. We argue that nonequilibrium electron occupancies of the $t_{2g}$ orbitals stabilized by applied current drive the observed lattice changes and thereby the novel phenomena in this system. Finally, we note that current-induced diamagnetism reported in recent literature [C. Sow et al., Science 358, 1084 (2017).] is not discerned in either slightly doped or pure ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$.

We report that $\mathrm{C}{\mathrm{u}}_9{\mathrm{O}}_2{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_4\mathrm{C}{\mathrm{l}}_6$ is a new multiferroic compound. Comprehensive studies of this compound have been carried out on single crystals as well as polycrystalline samples. Magnetic susceptibility $\chi$ and specific heat $C$ with $H\parallel c$ axis both reveal an anomaly at $T_N=37\mathrm{K}$ associated with the long-range antiferromagnetic order. However, no signature of this phase transition is seen with the $H\parallel b$ axis, providing evidence of the anisotropic nature of its magnetic properties. The results of $\chi$ measurements are consistent with the temperature evolution of the intensity of magnetic reflections from the neutron diffraction experiments. The magnetic structure derived from neutron scattering measurements shows that half of the Cu(5) ions carry no moments. Furthermore, an anomaly in the dielectric constant near $T_N$ and observable magnetoelectric coupling below $T_N$ are found. At high temperatures, a dielectric peak at $T_E=267\mathrm{K}$ is identified with no measurable spontaneous polarization below $T_E$, thereby suggesting an antiferroelectric order. A steplike anomaly seen in $\chi \left(T\right)$ at $T_E$ hints the weak spin-lattice coupling. Concomitantly, high-resolution temperature-dependent synchrotron x-ray diffraction experiments elucidate a local structural distortion at $T_E$.

Discovery of the new two-dimensional (2D) Dirac semimetals incorporating both superconductivity and the topological band structure has provided a novel platform for realizing the intriguing applications of Dirac fermions and Majorana quasiparticles, ranging from high-speed quantum devices at the nanoscale to topological quantum computations. In this work, utilizing first-principles calculations and symmetry analysis, we introduce $M\mathrm{OH}$ ($M=\text{Zr}$, Hf) as a new topological superconductor with Dirac points close to a Fermi level which are connected with nearly flat edge states as a striking feature of topological semimetals. Our calculations show that ZrOH as a 2D topological semimetal can exhibit superconductivity and is a novel platform for studying the interplay between superconductivity and Dirac states in low-dimensional materials.

We find that perpendicular electric fields can give rise to a tunable current-induced spin polarization in monolayer InSe. The interplay between the Rashba and the intrinsic Dresselhaus spin-orbit coupling leads to several Lifshitz transitions near the valence band maxima. Interestingly, the sign of the spin polarization changes with increasing perpendicular electric fields. We propose a spin potentiometric device to measure current-induced spin polarization.

Nonequilibrium states of a nanoscopic system may be achieved by both applying a bias voltage $V$ to its contacts and producing a difference $\mathrm{\Delta }T$ in their temperatures. Then the total current results from two competing flows, induced by $V$ and $\mathrm{\Delta }T$, respectively. Here we explore finite frequency quantum noise of this thermoelectric current flowing through a quantum dot whose low-energy dynamics is governed by Majorana degrees of freedom. We demonstrate that at finite frequency $\omega$ Majorana zero modes induce a perfect universal symmetry between photon emission and absorption spectra and produce universal thermoelectric resonances in their frequency dependence in contrast to non-Majorana quantum noise which is either asymmetric or nonuniversal. In particular, at low temperatures the differential thermoelectric quantum noise induced by Majorana zero modes shows resonances with a nontrivial maximum $\frac{e^3}{h}log\left(2^{1/4}\right)$ at $\omega =\mp \frac{\left|eV\right|}{\hslash }$ when $k_{\text{B}}\mathrm{\Delta }T\ll \left|eV\right|$. Our results challenge cutting-edge experiments using quantum noise detectors to reveal the universal spectral symmetry and resonant structure of the Majorana thermoelectric finite frequency quantum noise.

Applying coherent x rays using the method of atomic-scale x-ray photon correlation spectroscopy results in beam-induced dynamics in a number of oxide glasses. Here these studies are extended to rubidium and cesium borates with varying alkali contents. While no effect due to cumulative beam damage is observed, the observed rate of structural rearrangements shows a linear relation to the instantaneous dose rate. In agreement with the increasing glass transition temperature, the rate of dynamics at a given dose rate decreases with increasing alkali content, while the shape of the decay of correlations becomes progressively stretched. This behavior is explained in terms of faster dynamics of the alkali positions compared to the borate network. Finally, the $q$-dependent behavior of the correlation decay rate implies that the observed dynamics proceeds via small-scale atomic displacements subject to de Gennes narrowing.

By using a Fano resonance as one of the mirrors in an optical cavity, a localized mode with a highly asymmetric line shape is obtained. Placing a single quantum emitter inside the cavity leads to a new regime of cavity quantum electrodynamics, where the light-matter interaction dynamics is fundamentally different from that observed in a conventional cavity with Lorenztian line shape. Furthermore, when the vibrational dynamics of the emitter is taken into account, an intricate phonon-photon interplay arises, and the optical interference induced by the Fano mirror significantly alters the leakage of energy into vibrational modes. We demonstrate that this control mechanism improves the maximum attainable indistinguishability of emitted photons, as compared to an equivalent cavity with a conventional mirror.

When the impurity mean free path is short, only spin-polarized Cooper pairs which are nonlocally and antisymmetrically correlated in time may exist in a half-metallic ferromagnet. As a consequence, the half-metal acts as an odd-frequency superconducting condensate. We demonstrate both analytically and numerically that quantum vortices can emerge in half-metals despite the complete absence of conventional superconducting correlations. Because these metals are conducting in only one spin band, we show that a circulating spin supercurrent accompanies these vortices. Moreover, we demonstrate that magnetic disorder at the interfaces with the superconductor influences the position at which the vortices nucleate. This insight can be used to help determine the effective interfacial misalignment angles for the magnetization in hybrid structures since the vortex position is experimentally observable via scanning tunneling microscopy measurements. We also give a brief discussion regarding which superconducting order parameter to use for odd-frequency triplet Cooper pairs in the quasiclassical theory.

We propose a coupled-layer construction of a class of fracton topological orders in three spatial dimensions, which has no immobile excitations but is characterized by single quasiparticle excitations constrained in one-dimensional subspaces and dipole excitations mobile in two-dimensional subspaces. The simplest model is obtained by stacking and coupling layers of the two-dimensional toric codes on the square lattice and can be exactly solved in the strong-coupling limit. The resulting subdimensional excitations are understood as a consequence of anyon pair condensation induced by the coupling between layers. We also present generalizations of the construction for layers of the Kitaev-honeycomb models, the $Z_N$ toric codes, and the toric codes and the doubled semion models on the honeycomb lattice.

An electronic phase-field crystal model is proposed where the thermodynamics of electrons are considered in a free-energy-functional formulation. The free-electron-gas system is considered initially as the noninteracting limit of the model. The excess free-energy contribution to the functional is incorporated by including Coulombic repulsions among electrons and exchange-correlation interactions. The evolution of an electron mean field is considered in the low-temperature limit using diffusive dynamics. Three-dimensional Wigner crystallization can be achieved from the model when the density of the system is lowered sufficiently. Through this approach, we are able to provide insight into topological defect formation and evolution during Wigner crystallization.

We carried out first-principles calculations based on density functional theory aiming to understand the structural evolution along the stretching process and the impact of native defects in metallic subnanometer MoS nanowires (NWs). By pulling the pristine NWs quasistatically, we investigate the full structural evolution along the stretching process until the nanowire breaking point, obtaining a maximum applied stress (force) of $\approx 18.9$ GPa (7.1 nN). On the other hand, since the existence of intrinsic defects is likely to occur in these samples, we show that under S-rich conditions a sulfur antisite is found to be the energetically most stable defect, and under Mo-rich conditions a sulfur vacancy has the lowest formation energy. Our results also reveal that these defects present local reconstruction that can be clearly identified by the simulated scanning tunneling microscopy images. Furthermore, through a detailed analysis of the electronic structure, we verify that with the exception of the Mo interstitial and S antisite, all defects preserve the metallic behavior of the MoS nanowires.

We use an atomistic model to show that coupling between two nanowire quantum dots, forming an artificial molecule, can be used to control bright exciton splitting in these systems with external electric field and even reduce it to zero or reverse it. Importantly, strong interdot coupling allows this reduction to occur without a simultaneous detrimental reduction of excitonic optical activity, which is inherently present in weakly coupled systems. Our results indicate that nanowire quantum dot molecules could form a promising platform for quantum dot–based entanglement generation.