We discuss how the ideal rechargeable energy accumulator can be made and what the limits for solid-state energy storage are. We show that in theory, spin batteries based on heavy fermions can surpass chemical ones in terms of energy capacitance. The absence of chemical reactions in spin batteries makes them more stable, and also they do not need to be heated in cold conditions. We study how carrier statistics and the density of states affect the energy capacity of the battery. Also, we discuss hypothetical spin batteries based on neutron stars.

Recent experimental work shows that $\mathrm{Fe}\mathrm{P}{\mathrm{S}}_3$ undergoes phase transitions from $C2/m$ ($\beta \sim {107}^{\circ }$) to $C2/m$ ($\beta \sim {90}^{\circ }$) at 6 GPa and then to metallic $P\overline{3}1m$ at 14 GPa, with the magnetic ordering wave vector turning from $k=\left(01\frac{1}{2}\right)$ to $k=\left(010\right)$ at 2 GPa and to short-range magnetic order accompanying the insulator-metal transition. By preserving the magnetic point groups in ab initio calculations we report the following: (1) We successfully reproduce the first magnetic structure transition at 1.2 GPa and briefly discuss the influence of the Hubbard-$U$ parameter on this transition. This isostructural transition causes a change of the Brillouin zone from base-centered monoclinic to primitive monoclinic, and an indirect band gap to direct band gap transition. (2) There is a rotation of the Fe-S octahedron about $0.5^{\circ }$ through the [001] axis before the neighboring layers shift. (3) The shift between neighboring layers is predicted to occur at 10.0 GPa and reverses the energy order between $d_{x^2-y^2}$ and $d_{xy}$. (4) A sudden decrease of Fe-S bond length to 2.20 Å accompanies the vanishing of magnetic moment in the insulator-metal transition. Our work shows the importance of symmetries of magnetic structures in the pressure-induced phase transition of magnetic systems.

We report an experimental study on the tuning of supercurrent in a ballistic graphene-based Josephson junction by applying a control voltage to a transverse normal channel. In this four-terminal geometry, the control voltage changes the occupation of Andreev states in the Josephson junction, thereby tuning the magnitude of the supercurrent. As a function of gate voltage, we find two different regimes characterized by a double-step distribution and a hot-electron distribution, respectively. Our work opens opportunities to design highly controllable Josephson junctions for tunable superconducting quantum circuits.

We study the transport properties of a diffusive Josephson junction between two spin-split superconductors (SCs) made of SC-ferromagnetic insulator bilayers on top of a three-dimensional topological insulator. We derive the corresponding Usadel equation describing the quasiclassical Green's functions in these systems and first solve the equation analytically in the weak-proximity case. We demonstrate the appearance of an anomalous phase in the absence of an external magnetic field. We also explore nonreciprocal electronic transport. Specifically, we calculate the diode efficiency of the junction $\eta$ by solving the Usadel equation. We obtain a sizable diode effect even at zero applied magnetic field. We discuss how the diode efficiency $\eta$ depends on the different parameters and find a nonmonotonic behavior of $\eta$ with temperature.

Quantum effects of lattice vibration play a major role in many physical properties of condensed-matter systems, including thermal properties, such as specific heat, structural phase transition, as well as phenomena, such as quantum crystal and quantum paraelectricity that are closely related to zero-point fluctuations. However, realizing atomistic simulations for realistic materials with a fully quantum-mechanical description remains a great challenge. Here, we propose a first-principles strategy for large-scale molecular dynamics simulation, where a high-accuracy force field obtained by deep-potential (DP) is combined with quantum thermal bath (QTB) method to account for quantum effects. We demonstrate the power of this $\text{DP}+\text{QTB}$ method using the archetypal example $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$, which exhibits several phenomena induced by quantum fluctuations, such as the suppressed structure phase-transition temperature, the quantum paraelectric ground state at low temperatures and the quantum critical behavior $1/T^2$ law of dielectric constant. Our $\text{DP}+\text{QTB}$ strategy is efficient in simulating large-scale system and is first principles. More importantly, quantum effects of other systems could also be investigated as long as the corresponding DP model is trained. This strategy would greatly enrich our vision and means to study quantum behavior of condensed-matter physics.

$\mathrm{Pb}{\mathrm{Zr}}_{1-x}{\mathrm{Ti}}_x{\mathrm{O}}_3$ exhibits an antiferroelectric-ferroelectric phase boundary at the composition $x\sim 0.06$. Around this boundary, several questions need to be answered, such as the stabilizations of different phases with a small amount of compositional difference, the sequence of phase transitions, the coexistence of crystal structures, and potential applications. In this work, we have carried out systematic structural investigations of single crystals and ceramics with several compositions across the phase boundary. The phase diagram for $x\le 0.07$ has been established. A complex phase coexistence is found near the phase boundary, which leads to an unusual transition sequence. It is confirmed that $Pbam$ and $R3c$ structures maintain a subtle balance at the phase boundary, which may be perturbed by a slight change in the concentration or external stimuli. These findings provide unique insights into understanding the antiferroelectric-ferroelectric competition and, hence, into designing alternative materials for energy storage and conversion.

We investigate the localization of waves in aperiodic structures that manifest the characteristic multiscale complexity of arithmetic functions with a central role in number theory. In particular, we study the eigenspectra and wave localization properties of tight-binding Schrödinger equation models with onsite potentials distributed according to the Liouville function $\lambda \left(n\right)$, the Möbius function $\mu \left(n\right)$, and the Legendre sequence of quadratic residues modulo a prime. We employ multifractal detrended fluctuation analysis and establish the multifractal scaling properties of the energy spectra in these systems. Moreover, by systematically analyzing the spatial eigenmodes and their level spacing distributions, we show the absence of level repulsion with broadband localization across the entire energy spectra. Our study introduces finite-size aperiodic systems whose eigenmodes are all strongly localized and provide opportunities for unique quantum and classical devices of particular importance to cold-atom experiments with engineered speckle potentials as well as unique optical metamaterials and nanostructures with enhanced light-matter interactions.

We investigate spin and thermal transport near the Néel transition temperature $T_N$ in three dimensions by numerically analyzing the classical antiferromagnetic $XXZ$ model on the cubic lattice, where in the model, the anisotropy of the exchange interaction $\mathrm{\Delta }=J_z/J_x$ plays a role to control the universality class of the transition. It is found by means of the hybrid Monte Carlo and spin-dynamics simulations that in the $XY$ and Heisenberg cases of $\mathrm{\Delta }\le 1$, the longitudinal spin conductivity ${\sigma }_{\mu \mu }^s$ exhibits a divergent enhancement on cooling toward $T_N$ while not in the Ising case of $\mathrm{\Delta }>1$. In all three cases, the temperature dependence of the thermal conductivity ${\kappa }_{\mu \mu }$ is featureless at $T_N$, being consistent with experimental results. The divergent enhancement of ${\sigma }_{\mu \mu }^s$ toward $T_N$ is attributed to the spin-current relaxation time which gets longer toward $T_N$, showing a power-law divergence characteristic of critical phenomena. It is also found that in contrast to the $XY$ case where the divergence in ${\sigma }_{\mu \mu }^s$ is rapidly suppressed below $T_N, {\sigma }_{\mu \mu }^s$ likely remains divergent even below $T_N$ in the Heisenberg case, which might experimentally be observed in the ideally isotropic antiferromagnet ${\mathrm{RbMnF}}_3$.

The gap-opening mechanism of a topological insulator, the quantum anomalous Hall effect, and the axion physics are still pressing open questions, and a microscopic viewpoint to further understand the role of magnetism in topology is highly desirable. In this work we have performed a microscopic investigation, by means of electron spin resonance (ESR) along with complementary bulk measurements, on the chalcogenide ${\left({\mathrm{Bi}}_{1-x}{\mathrm{Gd}}_x\right)}_2{\mathrm{Se}}_3$ ($x=0$, 0.001, 0.002 and 0.006). Our analysis of the ${\mathrm{Gd}}^{3+}$ spin dynamics reveals no significant change of the Fermi surface as a function of ${\mathrm{Gd}}^{3+}$ concentration, which indicates that the $4f$ magnetism is different from the nonlocal effects induced by transition metal ($d$ electrons) substitutions. Additionally, we observe an unusual evolution of the ${\mathrm{Gd}}^{3+}$ ESR spectra as a function of the applied magnetic field, which we discuss considering the magnetic interaction between ${\mathrm{Gd}}^{3+}4f$ electrons and impurity centers such as Se vacancies. This interaction would give rise to a local weak antilocalization effect surrounding the ${\mathrm{Gd}}^{3+}$ ions. Such a mechanism is observable due to particular details of the ${\mathrm{Gd}}^{3+}4f$ electrons' magnetism in this system compared to that of $d$ electrons. Our work points out that rare-earth substitutions in this model topological insulator are a promising path to explore the axion insulating systems.

Using two-dimensional THz spectroscopy in combination with numerical models, we investigate the dynamics linked to carrier multiplication caused by high-field THz excitation of the low-gap semiconductor InSb. In addition to previously reported dynamics connected with quasiballistic carrier dynamics, we observe other spectral and temporal features that we attribute to impact ionization for peak fields above 60 kV/cm, which continue up to the maximum investigated peak field of 430 kV/cm. At the highest fields we estimate a carrier multiplication factor greater than 10 due to impact ionization, which is well-reproduced by a numerical simulation of the impact ionization process which we have developed.

We propose to synchronize Bloch oscillations in a double phase-slip junction by modulating the gate voltage rather than the bias voltage. We show this is advantageous, and the relatively small ac modulation of the gate voltage gives rise to the pronounced plateaus of quantized current of the width of the order of Coulomb blockade threshold. We theoretically investigate the setup distinguishing three regimes of strong, weak, and intermediate coupling, defined by the ratio of the gate capacitance $C$ and the effective capacitance of the phase-slip junctions. An important feature of the intermediate-coupling regime is the occurrence of the fractional plateaus of the quantized current. We investigate the finite temperature effects, finding an empirical scaling for the smoothing of integer plateaus.

We investigate the controversial case of the charge-density-wave (CDW) order in single-layer 1T-${\mathrm{TiSe}}_2$ by employing the density functional perturbation theory with on-site Hubbard interactions. The results emphasize the crucial role of electron correlations via Hubbard corrections in order to capture the accurate electronic structure, low- and high-temperature limits of the CDW phonon mode, and temperature-charge phase diagram. We show, in close agreement with the experiments, that the total phase diagram consists of both commensurate and incommensurate CDW regions, where the latter coincides with the superconductive phase and might be instrumental for its formation. In addition to the established roles of quantum lattice fluctuations and excitonic interactions, our analysis emphasizes the overlooked crucial role of the momentum-dependent electron-phonon coupling and electron correlations for the CDW phase transition in single-layer ${\mathrm{TiSe}}_2$.

Coherent thermal emission for a given polarization has been observed in many metamaterials with micro/nanostructures. Emissivity is typically obtained based on the equivalence between absorptivity and emissivity according to Kirchhoff's law; however, such a relationship may be invalid for nonreciprocal media. This study aims at developing a more general approach, without the constraint of optical reciprocity, that is applicable to magneto-optical materials and magnetic Weyl semimetals. A polarimetric analysis is theoretically carried out based on fluctuation electrodynamics to provide a complete description of the emissivity for all polarization states. The Stokes parameters are calculated from the coherency matrix for a multilayered system, which may include anisotropic media and even nonreciprocal materials. It is demonstrated that thermal emission may be circularly or linearly polarized in selected directions and frequencies. The findings of this work are consistent with the modified Kirchhoff's law provided by several groups in recent years, and therefore, justify the appropriateness of both the direct and indirect methods. This study will help the design of desired thermal emitters for energy harvesting and thermal control.

We study the suppression of the conductance quantization in quantum spin Hall systems by a combined effect of electronic interactions and edge disorder, that is ubiquitous in exfoliated and chemical vapor deposition grown two-dimensional (2D) materials. We show that the interplay between the electronic localized states due to edge defects and electron-electron interactions gives rise to local magnetic moments, that break time-reversal symmetry and the topological protection of the edge states in 2D topological systems. Our results suggest that edge disorder leads to small deviations of a perfect quantized conductance in short samples and to a strong conductance suppression in long ones. Our analysis is based on the Kane-Mele model, an unrestricted Hubbard mean-field Hamiltonian, and on a self-consistent recursive Green's function technique to calculate the transport quantities.

The presence of frozen uncorrelated random on-site potential in interacting quantum systems can induce a transition from an ergodic phase to a localized one, the so-called many-body localization. Here we numerically study the effects of autocorrelated disorder on the static and dynamical properties of a one-dimensional many-body quantum system which exhibits many-body localization. Specifically, by means of some standard measures of energy level repulsion and localization of energy eigenstates, we show that a strong degree of correlations between the on-site potentials in the one-dimensional spin-1/2 Heisenberg model leads to suppression of the many-body localization phase, while level repulsion is mitigated for small disorder strengths, although energy eigenstates remain well extended. Our findings are also remarkably manifested in the time domain, on which we put the main emphasis, as shown by the time evolution of experimentally relevant observables, like the return probability and the spin autocorrelation function.

Conservation laws and the associated hydrodynamic modes have important consequences on the growth of higher Rényi entropies in isolated quantum systems. It has been shown in various random unitary circuits and Hamiltonian systems that the dynamics of the Rényi entropies in the presence of a U(1) symmetry obey $S^{(n\ge 2)}\left(t\right)\propto t^{1/z}$, where $z$ is identified as the dynamical exponent characterizing transport of the conserved charges. Here, however, we demonstrate that this simple identification may not hold in certain quantum systems with kinetic constraints. In particular, we study two types of U(1)-symmetric quantum automaton circuits with XNOR (exclusive NOR) and Fredkin constraints, respectively. We find numerically that while spin transport in both models is subdiffusive, the second Rényi entropy grows diffusively in the XNOR model, and superdiffusively in the Fredkin model. For systems with the XNOR constraint, this distinction arises since the spin correlation function can be attributed to an emergent tracer dynamics of tagged particles, whereas the Rényi entropies are constrained by collective transport of the particles. Our results suggest that care must be taken when relating transport and entanglement entropy dynamics in generic quantum systems with conservation laws.

In addition to the topologically protected linear dispersion, a band-bending-confined two-dimensional electron gas with tunable Rashba spin-splitting (RSS) was found to coexist with the topological surface states on the surface of topological insulators (TIs). Here, we report the observation of large bilinear magnetoresistance (BMR) in ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ films decorated with transition-metal atoms. The magnitude of the BMR sensitively depends on the type and amount of atoms deposited, with a maximum achieved value close to those of strong Rashba semiconductors. Our first-principles calculations reproduce the quantum well states and reveal sizable RSS in all ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ heterostructures with broken inversion symmetry. Our results show that charge-spin interconversion through RSS states in TIs can be fine tuned through surface atom deposition and easily detected via BMR for potential spintronic applications.

The fundamental question of how information spreads in closed quantum many-body systems is often addressed through the lens of the bipartite entanglement entropy, a quantity that describes correlations in a comprehensive (nonlocal) way. Among the most striking features of the entanglement entropy are its unbounded linear growth in the thermodynamic limit, its asymptotic extensivity in finite-size systems, and the possibility of measurement-induced phase transitions, all of which have no obvious classical counterpart. Here, we show how these key qualitative features emerge naturally also in classical information spreading, as long as one treats the classical many-body problem on par with the quantum one, that is, by explicitly accounting for the exponentially large classical probability distribution. Our analysis is supported by extensive numerics on prototypical cellular automata and Hamiltonian systems, for which we focus on the classical mutual information and also introduce a “classical entanglement entropy.” Our study sheds light on the nature of information spreading in classical and quantum systems, and opens avenues for quantum-inspired classical approaches across physics, information theory, and statistics.

We study the physics of the Josephson effect in the odd-parity nematic superconductors within the Ginzburg-Landau approach. The order parameter is a two-component vector that transforms as a coordinate vector in the $(x,y)$ plane under rotation and its direction is usually refer to as the nematicity direction. A nontrivial interplay between the nematicity and crystallographic axes of the superconductors that form the junction makes the Josephson effect quite unusual. We derive current-phase relations for different configurations of the junction, crystallographic axes of the sample, and the nematicity direction in the superconductors. We obtain that the Meissner kernel in the considered samples has off-diagonal components and the transverse phase difference across the junction can induce a Josephson current that flows along the contact. We show that such an anomalous Josephson Hall effect can be observed without any magnetization. We calculate the magnetic field dependence of the maximum current through the junction. We find that the period of the Fraunhofer oscillations of the maximum Josephson current depends on the geometry of the junction, the direction of the magnetic field, and the nematicity directions. The obtained results can be generalized to other superconductors with nondiagonal Meissner kernels.