The recent discovery of a high critical temperature $T_c$ in compressed ${\mathrm{H}}_3\mathrm{S}$ has been followed by the prediction of Liu et al. of $T_c\approx 250$ K in the clathrate ${\mathrm{LaH}}_{10}$ structure. This report has been confirmed experimentally by Somayazulu et al. and Drozdov et al. Additional theoretical work by Wang et al. and Quan et al. further established the mechanism of electron-phonon interaction and the dominant role of hydrogen. In the present Rapid Communication we follow the classic McMillan paper, which separates the electron and phonon contributions to the electron-phonon coupling $\lambda$. We first compute the numerator of McMillan's expression, the Hopfield parameter $\eta$, using the theory of Gaspari and Gyorffy (GG), and obtain the force constants in the denominator from Wang et al. and Quan et al. The resulting $\lambda$ is used in the Allen-Dynes equation to calculate $T_c$. The value of $T_c$ reaches a maximum in the range of 236–263 K at pressures of 255 GPa and decreases for smaller or larger pressures. We provide a thorough analysis of the different terms of the GG equation and draw the conclusion that the $sp$ channel of the hydrogen is the most important contribution to obtain high values of $T_c$ in this material. Consistent with Wang et al., we find large values of $\lambda$ that decrease with increasing pressure. In addition, we find that the hydrogen sites are the largest contributors to the total value of the coupling constant $\lambda$. That is, the acoustic mode associated with La contributes only 2% to the total $\lambda$, while the optic modes associated with H contribute 18% for the H1 site and 80% for the H2 site. These relative contributions to $\lambda$ are consistent with those given by Wang et al. and by Quan et al. Thus, our results strongly support the view that ${\mathrm{LaH}}_{10}$ is a metallic hydrogen superconductor.

Multiply connected superconductors smaller than the coherence length show destructive superconductivity, characterized by reentrant quantum phase transitions driven by magnetic flux. We investigate the dependence of destructive superconductivity on flux, transverse magnetic field, temperature, and current in InAs nanowires with a surrounding epitaxial Al shell, finding excellent agreement with mean-field theory across multiple reentrant transitions. Near the crossover between destructive and nondestructive regimes, an anomalous metal phase is observed with temperature-independent resistance, controlled over two orders of magnitude by a millitesla-scale transverse magnetic field.

Entanglement features of the ground state of disordered quantum matter are often captured by an infinite-randomness fixed point that, for a variety of models, is the random singlet phase. Although a copious number of studies covers bipartite entanglement in pure states, at present, less is known for mixed states and tripartite settings. Our goal is to gain insights in this direction by studying the negativity spectrum in the random singlet phase. Through the strong disorder renormalization group technique, we derive analytic formulas for the universal scaling of the disorder-averaged moments of the partially transposed reduced density matrix. Our analytic predictions are checked against a numerical implementation of the strong disorder renormalization group and against exact computations for the XX spin chain (a model in which free fermion techniques apply). Importantly, our results show that the negativity and logarithmic negativity are not trivially related after the average over the disorder.

In this paper, we study the quantum criticality of Dirac fermions via large-scale numerical simulations, focusing on the Gross-Neveu-Yukawa chiral-Ising quantum critical point (QCP) with critical bosonic modes coupled with Dirac fermions. We show that finite-size effects at this QCP can be efficiently minimized via model design, which maximizes the ultraviolet cutoff and at the same time places the bare control parameters closer to the nontrivial fixed point to better expose the critical region. Combined with the efficient self-learning quantum Monte Carlo algorithm, which enables a nonlocal update of the bosonic field, we find that moderately large system size (up to $16\times 16$) is already sufficient to produce robust scaling behavior and critical exponents. The conductance of free Dirac fermions is also calculated, and its frequency dependence is found to be consistent with the scaling behavior predicted by the conformal field theory. The methods and model-design principles developed for this study can be generalized to other fermionic QCPs, and thus provide a promising direction for controlled studies of strongly correlated itinerant systems.

We describe a new universality class of dynamical quantum phase transitions of the Loschmidt amplitude of quantum spin chains off equilibrium criticality. We demonstrate that in many cases it is possible to change the conventional linear singularity of the Loschmidt rate function into a smooth peak by tuning one parameter of the quench protocol. Exactly at the point when this change-over occurs, the singularity of the Loschmidt rate function persists, with a critical exponent equal to $\frac{1}{2}$. The nonequilibrium renormalization group fixed point controlling this universality class is described. An asymptotically exact renormalization group recursion relation is derived around this fixed point to obtain the critical exponent.

The appearance of quasiparticle excitations with fractional statistics is a remarkable defining trait of topologically ordered systems. In this work we investigate the experimentally relevant finite-temperature regime in which one species of quasiparticle acts as a stochastic background for another, more energetically costly species that hops coherently across the lattice. The nontrivial statistical angle between the two species leads to interference effects that we study using a combination of numerical and analytical tools. In the limit of self-retracing paths, we are able to use a Bethe lattice approximation to construct exact analytical expressions for the time evolution of the site-resolved density profile of a spinon initially confined to a single site. Our results help us to understand the temperature-dependent crossover from ballistic to quantum (sub-) diffusive behavior as a consequence of destructive interference between lattice walks. The subdiffusive behavior is most pronounced in the case of semionic mutual statistics, and it may be ascribed to the localized nature of the effective tight-binding description, an effect that is not captured by the Bethe lattice mapping. In addition to quantum spin liquids, our results are directly applicable to the dynamics of isolated holes in the large-$U$ limit of the Hubbard model, relevant to ultracold atomic experiments. A recent proposal to implement ${\mathbb{Z}}_2$ topologically ordered Hamiltonians using quantum annealers provides a further exciting avenue to test our results.

Detailed analyses of the spin and orbital conductivities are performed for different topological phases of certain classes of two-dimensional multiorbital materials. Our calculations show the existence of orbital-Hall effect (OHE) in topological insulators, with values that exceed those obtained for the spin-Hall effect (SHE). Notably, we have found nontopological insulating phases that exhibit OHE in the absence of SHE. We demonstrate that the OHE in these systems is deeply linked to exotic momentum-space orbital textures that are triggered by an intrinsic Dresselhaus-type interaction that arises from a combination of orbital attributes and lattice symmetry. Our results strongly indicate that other classes of systems with nontrivial orbital textures and/or orbital magnetism may also exhibit large OHE even in their normal insulating phases.

Vilão et al. (Phys. Rev. B 96, 195205 (2017) and Phys. Rev. B 99, 195206 (2019)) have reported positive muon spin rotation/relaxation (${\mu }^{+}\mathrm{SR}$) experiments on various insulating metal oxides, solar cell materials, and alloyed Ge. They note the presence of a separate early component in the ${\mu }^{+}$ polarization time dependence which relaxes more rapidly than the longer lived signal and also exhibits (in ${\mathrm{ZrO}}_2$:Mg) a slightly increased frequency at low temperature in transverse field. They interpret this early component as a weakly bound “transition state” of the neutral muonium ($\mathrm{Mu}={\mu }^{+}{e}^{-}$) atom formed epithermally by the incoming 4-MeV muon, in which the hyperfine interaction between the muon and the electron is “motionally narrowed” by rapid spin exchange, resulting in a “diamagneticlike” Larmor precession signal. This “diamagneticlike transition state” supposedly takes microseconds to relax into its final ground state due to the reluctance of the surrounding lattice to deform around the Mu atom. However, numerous earlier experiments (including those in electric fields) on various liquids and solids ranging from wide-gap insulators to narrow-gap semiconductors have convincingly shown that Mu formation proceeds through capture of radiolysis electrons by thermalized muons—a process crucially dependent on the electron mobility rather than epithermal dynamics. Therefore, we question the validity of the interpretation by Vilão et al. and raise some important issues that need clarification.

The transition state model proposed for muonium formation in solids is critically discussed with respect to the delayed capture model. The two models differ mainly in how the electron capture at the muon is treated. In the delayed capture model the electron stems from the ionization track of the implanted muon. Important electron mobility information is derived in several papers from the time the electron needs to arrive at the muon. In our transition state model, the electron is picked up in the charge-exchange regime during slowing down and is present already when the muon stops in the target. Thus, no information about electron mobility can be obtained from such measurements.

High-order harmonic generation (HHG) has unleashed the power of strong laser physics in solids. Here we investigate HHG from a large system, solid ${\mathrm{C}}_{60}$, with 240 valence electrons engaging harmonic generation at each crystal momentum. We employ the density functional theory and the time-dependent Liouville equation of the density matrix to compute HHG signals. We find that under a moderately strong laser pulse, HHG signals reach 15th order, consistent with the experimental results from ${\mathrm{C}}_{60}$ plasma. The helicity dependence in solid ${\mathrm{C}}_{60}$ is weak, due to the high symmetry. In contrast to the general belief, HHG is unsuitable for band structure mapping in ${\mathrm{C}}_{60}$. However, we find a window of opportunity using a long wavelength, where harmonics are generated through multiple-photon excitation. In particular, the fifth-order harmonic energies closely follow the transition energy dispersion between the valence and conduction bands. This finding is expected to motivate future experimental investigations.

We propose a many-body index that extends Fredholm index theory to many-body systems. The index is defined for any charge-conserving system with a topologically ordered $p$-dimensional ground-state sector. The index is fractional, with the denominator given by $p$. In particular, this yields a short proof of the quantization of the Hall conductance and of the Lieb-Schulz-Mattis theorem. In the case that the index is not an integer, the argument provides an explicit construction of Wilson loop operators exhibiting a nontrivial braiding that can be used to create fractionally charged Abelian anyons.

We investigate the effect on the entanglement dynamics of an impurity moving at a constant velocity in a closed quantum system. We focus on one-dimensional strongly correlated lattice models, both in the presence of integrable and chaotic dynamics. In the former, the slow impurity is preceded by fast quasiparticles carrying an endogenous entanglement front which decays in time as a power law; on the contrary, a fast impurity drags itself an exogenous entanglement front which never fades. We argue that these effects are valid for generic systems whose correlations propagate inside a light cone. To assess the fully chaotic regime, we formulate a random circuit model which supports a moving impurity and a sharp light cone. Although the qualitative behavior is similar to the integrable case, the endogenous regime is only visible at short times due to the onset of diffusive energy transport. Our predictions are supported by numerical simulations in the different regimes.

Methylammonium lead halide $\left({\mathrm{MAPbI}}_3\right)$ perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-$⊠)$ are addressed in regulating stability and solar cell efficiency of ${\mathrm{MAPb}}_{1-X-Y}{\mathrm{Sn}}_X{⊠}_Y{\mathrm{I}}_3$ perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron's self-interaction error are examined carefully. We find to reduce the Pb content from pristine ${\mathrm{MAPbI}}_3$, Sn substitution has a more favorable thermodynamic stability than creating Pb-$⊠$. Moreover, on substituting Sn, due to strong $s\text{−}p$ and $p\text{−}p$ couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coefficient (redshifted) and maximum solar cell efficiency in ${\mathrm{MAPb}}_{1-X}{\mathrm{Sn}}_X{\mathrm{I}}_3$ for $0<X\le 0.5$.

Moiré superlattices form in twisted graphene bilayers due to periodic regions of commensurability, but truncation of the moiré patterns affects the rotational stability of finite-sized sheets. Here, we report the stepwise untwisting of nanometer-sized bilayer graphene flakes at elevated temperatures, each step corresponding to a potential energy barrier formed by changes to the commensurability between the moiré superlattice and flake size with twist angle. The number of locally stable energy states and their barrier energies scale with the flake size, allowing twisted graphene flakes of several tens of nanometers to remain thermally stable even at chemical vapor deposition temperatures.

We consider here the possibility of shaping the high-frequency acoustic propagation in a liquid upon directional confinement. This hypothesis is investigated by inelastic x-ray scattering measurements on water confined in aligned multiwalled carbon nanotubes, in which the momentum transfer was either parallel or orthogonal to the confinement axis. The comparison between the spectra measured in these two scattering geometries highlights the anisotropic nature of the dynamic response of directionally confined water, thus potentially inspiring pathways to shape high-frequency sound propagation in isotropic systems. Finally, a Bayesian analysis of measured spectra unravels close similarities in the phonon dispersions of multiwalled nanotubes and graphite.

An orthorhombic compound, $\mathrm{NaMnSb}{\mathrm{O}}_4$, represents a square net of magnetic $\mathrm{M}{\mathrm{n}}^{2+}$ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and density-functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with $T_{\mathrm{N}}\sim 44\mathrm{K}$, which is preceded by a short-range one at about 55 K. In addition, a nontrivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of two-dimensional square-lattice model with the main exchange parameter $J=-5.3\mathrm{K}$, which is in good agreement with density-functional analysis, NMR, and ESR data.

We demonstrate a modulation of up to $18\%$ in the magnon spin transport in a magnetic insulator $({\text{Y}}_3{\text{Fe}}_5{\text{O}}_{12}$, YIG) using a common ferromagnetic metal (permalloy, Py) as a magnetic control gate. A Py electrode, placed between two Pt injector and detector electrodes, acts as a magnetic gate in our prototypical magnon transistor device. By manipulating the magnetization direction of Py with respect to that of YIG, the transmission of magnons through the $\mathrm{Py}\mid \mathrm{YIG}$ interface can be controlled, resulting in a modulation of the nonequilibrium magnon density in the YIG channel between the Pt injector and detector electrodes. This study opens up the possibility of using the magnetic gating effect for magnon-based spin logic applications.

We study the influence of a strong off-resonant driving signal to the energy levels of a superconducting flux qubit both experimentally and theoretically. In the experiment, we carry out a three-tone spectroscopy. This allows us to directly observe the modification of the qubit's energy levels by the dynamical Stark shift caused by the driving signal. A theoretical treatment including corrections from both rotating and counter-rotating frames, allowed us to completely explain the observed experimental results and to reconstruct the influence of the strong driving to the dissipative dynamics as well as to the coupling constants of the qubit. As one potential application, the tunability of the minimal energy-level splitting of a superconducting qubit by a microwave-induced dynamical Stark shift can help to overcome the parameter spread induced by the microfabrication of superconducting artificial quantum circuits.

We investigate the proximity effect in a heterostructure of the topological insulator (TI) ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ deposited on the high-temperature superconductor (HTSC) material ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$. The latter is described by the one-band Hubbard model and is treated with cluster dynamical mean field theory (CDMFT), the topological insulator (TI) layers being included via the CDMFT self-consistency loop. The penetration of superconductivity into the TI depends on the position of the Fermi level with respect to the TI gap. We illustrate the back action of the TI layer on the HTSC layer, in particular the gradual disappearance of Mott physics with increasing tunneling amplitude.