We report the observation of anomalous Hall resistivity in single crystals of ${\mathrm{EuAl}}_4$, a centrosymmetric tetragonal compound, which exhibits coexisting antiferromagnetic (AFM) and charge-density-wave (CDW) orders with onset at $T_{\mathrm{N}}\sim 15.6\mathrm{K}$ and $T_{\mathrm{CDW}}\sim 140\mathrm{K}$, respectively. In the AFM state, when the magnetic field is applied along the $c$-axis direction, ${\mathrm{EuAl}}_4$ undergoes a series of metamagnetic transitions. Within this field range, we observe a clear humplike anomaly in the Hall resistivity, representing part of the anomalous Hall resistivity. By considering different scenarios, we conclude that such a humplike feature is most likely a manifestation of the topological Hall effect, normally occurring in noncentrosymmetric materials known to host nontrivial topological spin textures. In view of this, ${\mathrm{EuAl}}_4$ would represent a rare case where the topological Hall effect not only arises in a centrosymmetric structure, but it also coexists with CDW order.

Thermally induced magnetization dynamics is currently a flourishing field of research due to its potential application in information technology. We study the paradigmatic system of a magnetic domain wall in a thermal gradient which is interacting with an adjacent superconductor. The spin-transfer torques arising in this system due to the combined action of the giant thermoelectric effect and the creation of equal-spin pairs in the superconductor are large enough to give rise to high domain wall velocities ${10}^3$ times larger than previously predicted.

We use exact quantum Monte Carlo simulations to demonstrate that the Néel ground state of an antiferromagnetic SU(2) spin-$\frac{1}{2}$ Heisenberg model on the honeycomb lattice can be destroyed by a coupling to quantum phonons. We find a clear first-order transition to a valence bond solid state with Kekulé order instead of a deconfined quantum critical point. However, quantum lattice fluctuations can drive the transition towards weakly first order, revealing a tunability of the transition by the retardation of the interaction. In contrast to the one-dimensional case, our phase diagram in the adiabatic regime is qualitatively different from the frustrated $J_1\text{−}{J}_2$ model. Our results suggest that a coupling to bond phonons can induce Kekulé order in Dirac systems.

Calculations of heat transfer between two plates of gold in an extreme near field is performed taking into account the existence of the electrical double layer on metal surfaces. For $d<3\mathrm{nm}$ the double layer contribution to the heat flux exceeds the predictions of the conversional theory of the heat transfer by several orders of magnitudes. The predicted effect is not related with bias voltage but occurs due to intrinsic properties of the electrical double layer. The results obtained can be used for the heat management at the nanoscale by intentionally changing the parameters of surface dipoles with the help of engineering.

Bragg coherent diffractive imaging (BCDI) is a noninvasive microscopy technique that can visualize the morphology and internal lattice deviations of crystals with nanoscale spatial resolution and picometer deformation sensitivity. While BCDI has been successfully applied in various studies of materials, it is less successful for highly strained crystals. Specifically, it is difficult to correctly reconstruct the electron density of a highly strained object using conventional phase retrieval algorithms. Although various algorithms have been developed to overcome this challenge, most of them require a priori knowledge that is not always available in practice. Here we report a phase retrieval workflow that can invert diffraction patterns from multiple Bragg peaks simultaneously. The workflow is explored via simulated diffraction from crystals with various strain conditions. Reconstructions from the workflow consistently demonstrate more accurate electron density maps, in comparison with the conventional method. For highly strained crystals, the workflow improves the reliability and consistency of BCDI phase retrieval significantly.

Utilizing the synchrotron x-ray powder diffraction ${\mathrm{As}}_2{\mathrm{Se}}_3$ has been investigated under high pressure in a diamond anvil cell with hydrogen and neon applied as the pressure media. For both systems the amorphous samples were compressed to ca. 2–3 GPa and heated in situ by a laser, which led to their crystallization in the $R$-3 $m, {\mathrm{Bi}}_2{\mathrm{Te}}_3$-type phase. During further compression this phase transforms to the $C2/m, \beta \text{−}{\mathrm{Sb}}_2{\mathrm{Te}}_3$-type structure, and they coexist within the pressure range of 21.5–33.0 GPa. The latter phase is observed up to the highest achieved pressure of 52.0 GPa, revealing no signs of reaction with the hydrogen pressure-transmitting medium. The pressure evolution of the volume of the reported phases has been described by the third-order Birch-Murnaghan equation of state. The relative stability of the experimentally detected crystalline phases is confirmed by the density functional theory calculations. The pressure-driven evolution of the As–Se distances and coordination number has been discussed in comparison to the recent findings concerning the amorphous $a\text{−}{\mathrm{As}}_2{\mathrm{Se}}_3$ phase.

Quantum phase estimation is at the heart of most quantum algorithms with exponential speedup. In this paper we demonstrate how to utilize it to compute the dynamical response functions of many-body quantum systems. Specifically, we design a circuit that acts as an efficient quantum generative model, providing samples out of the spectral function of high rank observables in polynomial time. This includes many experimentally relevant spectra such as the dynamic structure factor, the optical conductivity, or the NMR spectrum. Experimental realization of the algorithm, apart from logarithmic overhead, requires doubling the number of qubits as compared to a simple analog simulator.

For non-Hermitian quantum models, the dynamics is apparently not reflected by the static properties, e.g., the complex energy spectrum, because of the nonorthogonality of the right eigenvectors, the nonunitarity of the time evolution, the breakdown of the adiabatic theory, etc., but in experiments the time evolution of an initial state is commonly used. Here, we pay attention to the dynamics of an initial end state in nonreciprocal Su-Schrieffer-Heeger models under open boundary conditions, and we find that it is dynamically more robust than its Hermitian counterpart, because the non-Hermitian skin effect can suppress the part leaking to the bulk sites. To observe this, we propose a classical electric circuit with only a few passive inductors and capacitors, the mapping of which to the quantum model is established. This work explains how the non-Hermitian skin effect enhances the robustness of the topological end state, and it offers an easy way, via the classical electric circuit, of studying the nonreciprocal quantum dynamics, which may stimulate more dynamical studies of non-Hermitian models in other platforms.

We investigated the magnetoelastic properties of the quasi-one-dimensional spin-$\frac{1}{2}$ frustrated magnet ${\mathrm{LiCuVO}}_4$. Longitudinal-magnetostriction experiments were performed at 1.5 K in high magnetic fields of up to 60 T applied along the $b$ axis, i.e., the spin-chain direction. The magnetostriction data qualitatively resemble the magnetization results, and saturate at $H_{\text{sat}}\approx 54$ T, with a relative change in sample length of $\mathrm{\Delta }L/L\approx 1.8\times {10}^{-4}$. Remarkably, both the magnetostriction and the magnetization evolve gradually between $H_{\text{c3}}\approx 48$ T and $H_{\text{sat}}$, indicating that the two quantities consistently detect the spin-nematic phase just below the saturation. Numerical analyses for a weakly coupled spin-chain model reveal that the observed magnetostriction can overall be understood within an exchange-striction mechanism. Small deviations found may indicate nontrivial changes in local correlations associated with the field-induced phase transitions.

Nonmagnetic impurity scattering effects in the vortex states are studied in the Born and the unitary limits for chiral superconductors by Eilenberger theory. We compare the spatial structure of the pair potential and local electronic structure in chiral $p$-wave superconductors with those in two types of chiral $d$-wave superconductors; $d_{1\pm }\equiv d_{xz}\pm i{d}_{yz}$ and $d_{2\pm }\equiv d_{x^2-y^2}\pm i{d}_{xy}$ pairing. Similar behaviors of the pair potentials are seen in $p_{\pm }$- and $d_{1\pm }$-wave superconductors. In chiral $d$-wave superconductors, due to lack of Majorana properties relating to the $s$-wave Cooper pair amplitude, zero-energy vortex bound states are easily destroyed by the impurity scattering, compared to the Born limit in the chiral $p_{-}$-wave superconductors. This decay is also seen in the unitary limit in the chiral $p_{-}$-wave superconductors. These differences are also discussed in the relation to $s$-wave Cooper pair amplitude and the local scattering rate. The impurity effects are also compared with those in $s$-wave superconductors.

Recently, direct band gap double perovskites have become more popular among the photovoltaic research community owing to their potential to address issues of lead toxicity and structural instability inherent in lead halide (simple) perovskites. In this study, an In-Ag-based direct band gap double perovskite, ${\mathrm{Cs}}_2{\mathrm{AgInCl}}_6$ (CAIC), is treated with transition metal doping to improve the optoelectronic properties of the material. Investigations of the structural and optoelectronic properties of Cu-doped CAIC, ${\mathrm{Cs}}_2{\mathrm{Ag}}_{(1-x)}{\mathrm{Cu}}_x{\mathrm{InCl}}_6$, are done using ab initio calculations with density functional theory and virtual crystal approximation. Our calculations show that with increasing Cu content, the optimized lattice parameter and direct band gap of ${\mathrm{Cs}}_2{\mathrm{Ag}}_{(1-x)}{\mathrm{Cu}}_x{\mathrm{InCl}}_6$ decrease following linear and quadratic functions, respectively, while the bulk modulus increases following a quartic polynomial function. The photoabsorption coefficient, optical conductivity, and other optical parameters of interest are also computed, and the obtained spectra indicate enhanced optical properties at higher Cu contents. Based on our results, transition metal (Cu) doping is a viable means of treating double perovskites, by tuning their optoelectronic properties to be suitable for an extensive range of photovoltaics, solar cells, and optoelectronics.

Layered trigonal ${\mathrm{EuMg}}_2{\mathrm{Bi}}_2$ is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature $\chi \left(T\right)$ of ${\mathrm{EuMg}}_2{\mathrm{Bi}}_2$ that show the intraplane ordering is ferromagnetic (${\mathrm{Eu}}^{2+},S=7/2$) with the moments aligned in the $ab$ plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the Néel temperature.

The one-dimensional transverse field Ising model with boundary fields is studied analytically and numerically. The phase diagram in the ordered state is obtained. We find that there exist two types of phase transitions. The longitudinal boundary fields applied to the left and right ends of the Ising chain are $h_L$ and $h_R$, respectively. For $|h_L|,|h_R|<\sqrt{1-g}$, where $g$ is the transverse field and $h_L{h}_R<0$, a first-order phase transition occurs with the changing $h_L$ or $h_R$. The energy gap and boundary magnetization are solved exactly. The analytical expressions of the finite-size scaling for the first-order phase transition are obtained. For $|h_R|>\sqrt{1-g}$ and $h_L{h}_R<0$, there exists a continuous phase transition with changing $h_L$ and vice versa. This transition is identified as a quantum wetting transition. The singularity of the boundary magnetization in this phase transition is explicitly shown. A simple computational procedure with high accuracy and efficiency is proposed to calculate the magnetization. The magnetization profile, correlation functions, and wetting layer thickness are studied numerically.

We report the high-field superconducting properties of thin, disordered Re films via magnetotransport and tunneling density of states measurements. Films with thicknesses in the range of 9 to 3 nm had normal-state sheet resistances of $\sim 0.2\mathrm{k}\mathrm{\Omega }$ to $\sim 1\mathrm{k}\mathrm{\Omega }$ and corresponding transition temperatures in the range of 6 to 3 K. Tunneling spectra were consistent with those of a moderate coupling BCS superconductor. Notwithstanding these unremarkable superconducting properties, the films exhibited an extraordinarily high upper critical field. We estimate their zero temperature $H_{c2}$ to be more than twice the Pauli limit. Indeed, in 6-nm samples the estimated reduced critical field $H_{c2}/T_c\sim 5.6\mathrm{T}/\mathrm{K}$ is among the highest reported for any elemental superconductor. Although the sheet resistances of the films were well below the quantum resistance $R_Q=h/4e^2$, their $H_{c2}$'s approached the theoretical upper limit of a strongly disordered superconductor for which $k_F\ell \sim 1$.

Boron is an intriguing element due to its electron deficiency and the ability to form multicenter bonds in allotropes and borides, exhibiting diversified structures, unique chemical bonds, and interesting properties. Using swarm-intelligence structural prediction driven by a machine learning potential, we identified a boron phase with a 24-atom cubic unit cell, called $c\text{−}{\mathrm{B}}_{24}$, consisting of a ${\mathrm{B}}_6$ octahedron in addition to well-known ${\mathrm{B}}_2$ pairs and ${\mathrm{B}}_{12}$ icosahedra at ambient pressure. There appear unusual four-center-two-electron (4c-2e) bonds in the ${\mathrm{B}}_{12}$ icosahedron, originating from the peculiar bonding pattern between the ${\mathrm{B}}_2$ pair and ${\mathrm{B}}_{12}$ icosahedron, which is in sharp contrast with the 3c-2e and 2c-2e bonds in $\alpha \text{−}{\mathrm{B}}_{12}$. More interestingly, $c\text{−}{\mathrm{B}}_{24}$ is a metal with a superconducting critical temperature of 13.8 K at ambient pressure. The predicted Vickers hardness (23.1 GPa) indicates that $c\text{−}{\mathrm{B}}_{24}$ is a potential hard material. Notably, it also has a good shear/tensile resistance (48.9/29.3 GPa). Our work not only enriches the understanding of the chemical properties of boron, but also sparks efforts on trying to synthesize this particular compound, $c\text{−}{\mathrm{B}}_{24}$.

We study high-harmonic generation (HHG) in the one-dimensional Hubbard model in order to understand its relation to elementary excitations as well as the similarities and differences to semiconductors. The simulations are based on the infinite time-evolving block decimation (iTEBD) method and exact diagonalization. We clarify that the HHG originates from the doublon-holon recombination, and the scaling of the cutoff frequency is consistent with a linear dependence on the external field. We demonstrate that the subcycle features of the HHG can be reasonably described by a phenomenological three step model for a doublon-holon pair. We argue that the HHG in the one-dimensional Mott insulator is closely related to the dispersion of the doublon-holon pair with respect to its relative momentum, which is not necessarily captured by the single-particle spectrum due to the many-body nature of the elementary excitations. For the comparison to semiconductors, we introduce effective models obtained from the Schrieffer-Wolff transformation, i.e., a strong-coupling expansion, which allows us to disentangle the different processes involved in the Hubbard model: intraband dynamics of doublons and holons, interband dipole excitations, and spin exchanges. These demonstrate the formal similarity of the Mott system to the semiconductor models in the dipole gauge, and reveal that the spin dynamics, which does not directly affect the charge dynamics, can reduce the HHG intensity. We also show that the long-range component of the intraband dipole moment has a substantial effect on the HHG intensity, while the correlated hopping terms for the doublons and holons essentially determine the shape of the HHG spectrum. A new numerical method to evaluate single-particle spectra within the iTEBD method is also introduced.

We report a microscopic electronic mechanism for nanoscale skyrmion formation and topological metalicity originating from Rashba and double-exchange physics. The results are based on hybrid simulations in a model that explicitly retains itinerant electronic degrees of freedom. A simple physical picture is provided via an effective short-range spin model. We identify hexagonal and square lattice arrangements of skyrmions in two different regimes of the parameter space. Sparse skyrmions emerge at finite temperatures as excitations of the ferromagnetic phase. The skyrmion states are characterized as topological metals via explicit calculations of the Bott index and the Hall conductivity. Oscillations in local density of states are shown to arise from a combination of confinement effects and emergent gauge-fields. We also emphasize the importance of a consistent treatment of spin-orbit coupling for calculating electronic properties of metals hosting unconventional magnetic textures such as skyrmions.

We propose entangling operations based on the energy curvature couplings of encoded spin qubits to a superconducting cavity, exploring the nonlinear qubit response to a gate voltage variation. For a two-qubit ($n$-qubit) entangling gate we explore acquired geometric phases via a time-modulated longitudinal ${\sigma }_z$ coupling, offering gate times of tens of nanoseconds even when the qubits and the cavity are far detuned. No dipole moment is necessary: the qubit transverse ${\sigma }_x$ coupling to the resonator is zero at the full sweet spot of the encoded spin qubit of interest (a triple quantum dot three-electron exchange-only qubit or a double quantum dot singlet-triplet qubit). This approach allows always-on, exchange-only qubits, for example, to stay on their “sweet spots” during gate operations, minimizing the charge noise and eliminating an always-on static longitudinal qubit-qubit coupling. We calculate the main gate errors due to the (1) diffusion (Johnson) noise and (2) damping of the resonator, the (3) $1/f$-charge noise qubit gate dephasing and $1/f$ noise on the longitudinal coupling, (4) qubit dephasing and AC-Stark frequency shifts via photon fluctuations in the resonator, and (5) spin-dependent resonator frequency shifts (via a “dispersivelike” static curvature coupling), most of them associated with the nonzero qubit energy curvature (quantum capacitance). Using spin-echo-like error suppression at optimal regimes, gate infidelities of ${10}^{-2}–{10}^{-3}$ can be achieved with experimentally existing parameters. The proposed schemes seem suitable for remote spin-to-spin entanglement of two spin qubits or a cluster of spin qubits: an important resource of quantum computing.