Recently, a generic model was proposed for the single-particle properties of gapless superconductors with simultaneously present pair-conserving and pair-breaking impurity scatterings (the so-called Dynes superconductors). Here we calculate the optical conductivity of the Dynes superconductors. Our approach is applicable for all disorder strengths from the clean limit up to the dirty limit and for all relative ratios of the two types of scattering; nevertheless, the complexity of our description is equivalent to that of the widely used Mattis-Bardeen theory. We identify two optical fingerprints of the Dynes superconductors: (i) the presence of two absorption edges and (ii) finite absorption at vanishing frequencies even at the lowest temperatures. We demonstrate that the recent anomalous optical data on thin MoN films can be reasonably fitted by our theory.

We investigate the effect of Rashba splitting on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in a topological-insulator (TI) thin film both at finite and zero chemical potential. We show that the spin susceptibility of the TI thin film depends strongly on the direction of the distance vector between impurities. In addition to the well-known Heisenberg-, Ising-, and Dzyaloshinskii-Moria (DM)-like terms reported before in TIs, we find another term in the off-diagonal part of the spin-susceptibility tensor which is symmetric in contrast to the DM term. Furthermore, we show how one can tune the RKKY interaction by using electric field applied perpendicularly to the surface plane of the TI, where in the presence of such a field the RKKY interaction can be enhanced drastically for small chemical doping. We present our results for two different situations, namely intersurface pairing of magnetic impurities as well as intrasurface pairing. The behavior of these two situations is completely different, which we describe by mapping the density of states of each surface on the band dispersion.

Spin pumping refers to the microwave-driven spin current injection from a ferromagnet into the adjacent target material. We theoretically investigate the spin pumping into superconductors by fully taking account of impurity spin-orbit scattering that is indispensable to describe diffusive spin transport with finite spin diffusion length. We calculate temperature dependence of the spin pumping signal and show that a pronounced coherence peak appears immediately below the superconducting transition temperature $T_{\mathrm{c}}$, which survives even in the presence of the spin-orbit scattering. The phenomenon provides us with a new way of studying the dynamic spin susceptibility in a superconducting thin film. This is contrasted with the nuclear magnetic resonance technique used to study a bulk superconductor.

While macroscopic properties of spin glasses have been thoroughly investigated, their manifestation in the corresponding microscopic configurations is much less understood. Cases where both descriptions have been provided, such as constraint satisfaction problems, are limited to their ground state properties. To identify the emerging microscopic structures with macroscopic phases at different temperatures, we study the $p$-spin model with $p=3$. We investigate the properties of self-sustained clusters, defined as variable sets where in-cluster-induced fields dominate over the fields induced by out-cluster spins, giving rise to stable configurations with respect to fluctuations. We compute the entropy of self-sustained clusters as a function of temperature and their sizes. In-cluster and out-cluster field properties support the observation of slow-evolving spins in spin models. These findings are corroborated by numerical studies in finite-size systems at low temperatures.

The spin dynamics in the distorted triangular lattice antiferromagnet $\alpha -{\mathrm{SrCr}}_2{\mathrm{O}}_4$ has been investigated by inelastic neutron scattering on a single crystal. The spin wave dispersion has been mapped out in the $\left(0kl\right)$ and $\left(hk0\right)$ planes, and modeled by spin wave calculations, in order to determine the intraplane and interplane exchange couplings. Comparison with $\alpha -{\mathrm{CaCr}}_2{\mathrm{O}}_4$ shows that, despite the smaller lattice distortion of $\alpha -{\mathrm{SrCr}}_2{\mathrm{O}}_4$, the deviation from a perfect triangular lattice still affects the spin dynamics of the Sr compound, with a soft mode, similar to the one observed in the Ca counterpart, being observed in (020). Although $\alpha -{\mathrm{SrCr}}_2{\mathrm{O}}_4$ is further away from a magnetic phase boundary than its Ca counterpart, its dynamic magnetic properties still show intriguing features, which are discussed as quantum fluctuations arising from a two-magnon continuum.

The magnetic structure of $\mathrm{L}{\mathrm{i}}_3\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$ has been determined by low-temperature neutron diffraction, and the crystal structure has been refined by a combination of synchrotron and neutron powder diffraction. The monoclinic ($C2/m$) symmetry, assigned previously to this pseudohexagonal layered structure, has been unambiguously proven by peak splitting in the synchrotron diffraction pattern. The structure is based on essentially hexagonal honeycomb-ordered $\mathrm{N}{\mathrm{i}}_2\mathrm{Sb}{\mathrm{O}}_6$ layers alternating with $\mathrm{L}{\mathrm{i}}_3$ layers, all cations and anions being in an octahedral environment. The compound orders antiferromagnetically below $T_{\mathrm{N}}=15\mathrm{K}$, with the magnetic supercell being a $2a\times 2b$ multiple of the crystal cell. The magnetic structure within the honeycomb layer consists of zigzag ferromagnetic spin chains coupled antiferromagnetically. The ordered magnetic moment amounts to $1.62\left(2\right){\mu }_{\mathrm{B}}/\mathrm{Ni}$, which is slightly lower than the full theoretical value. Upon cooling below $T_{\mathrm{N}}$, the spins tilt from the $c$ axis, with a maximum tilting angle of $15.6^{\circ }$ at $T=1.5\mathrm{K}$. Our data imply non-negligible ferromagnetic interactions between the honeycomb layers. The observed antiferromagnetic resonance modes are in agreement with the two-sublattice model derived from the neutron data. Orthorhombic anisotropy shows up in zero-field splitting of $\mathrm{\Delta }=198\pm 4$ and $218\pm 4\mathrm{GHz}$. Above $T_{\mathrm{N}}$, the electron spin resonance data imply short-range antiferromagnetic order up to about 80 K.

The pairing symmetry of the cobalt high-temperature (high-$T_c$) superconductors formed by vertex-shared cation-anion tetrahedral complexes is studied by the methods of mean-field, random phase approximation (RPA), and functional renormalization-group (FRG) analyses. The results of all of these methods show that the $d_{x^2-y^2}$ pairing symmetry is robustly favored near half filling. The RPA and FRG methods, which are valid in weak-interaction regions, predict that the superconducting state is also strongly orbital selective, namely, the $d_{x^2-y^2}$ orbital that has the largest density near half filling among the three $t_{2g}$ orbitals dominates superconducting pairing. These results suggest that these materials, if synthesized, can provide an indisputable test of the high-$T_c$ pairing mechanism and the validity of different theoretical methods.

We calculate the universal contribution to the $\alpha$-Rényi entropy from a cubic trihedral corner in the boundary of the entangling region in $3+1$ dimensions for a massless free scalar. The universal number $v_{\alpha }$ is manifest as the coefficient of a scaling term that is logarithmic in the size of the entangling region. Our numerical calculations find that this universal coefficient has both larger magnitude and the opposite sign to that induced by a smooth spherical entangling boundary in $3+1$ dimensions, for which there is a well-known subleading logarithmic scaling. Despite these differences, up to the uncertainty of our finite-size lattice calculations, the functional dependence of the trihedral coefficient $v_{\alpha }$ on the Rényi index $\alpha$ is indistinguishable from that for a sphere, which is known analytically for a massless free scalar. We comment on the possible source of this $\alpha$ dependence arising from the general structure of $(3+1)$-dimensional conformal field theories, and suggest calculations past the free scalar which could further illuminate the general structure of the trihedral divergence in the Rényi entropy.

The Kagome-lattice-based material, volborthite, ${\mathrm{Cu}}_3{\mathrm{V}}_2{\mathrm{O}}_7{\left(\mathrm{OH}\right)}_2·2{\mathrm{H}}_2\mathrm{O}$, has been considered as a promising platform for discovery of unusual quantum ground states due to the frustrated nature of spin interaction. We explore possible quantum spin liquid and magnetically ordered phases in a two-dimensional nonsymmorphic lattice, which is described by the plane group $p2gg$, consistent with the spatial anisotropy of the spin model derived from density functional theory (DFT) for volborthite. Using the projective symmetry group (PSG) analysis and Schwinger boson mean field theory, we classify possible spin liquid phases with bosonic spinons and investigate magnetically ordered phases connected to such states. It is shown, in general, that only translationally invariant mean field spin liquid ansatzes are allowed in two-dimensional nonsymmorphic lattices. We study the mean field phase diagram of the DFT-derived spin model and find that possible quantum spin liquid phases are connected to two types of magnetically ordered phases, a coplanar incommensurate $(q,0)$ spiral order as the ground state and a closely competing coplanar commensurate $(\pi ,\pi )$ spin density wave order. In addition, periodicity enhancement of the two-spinon continuum, a consequence of symmetry fractionalization, is found in the spin liquid state connected to the $(\pi ,\pi )$ spin density wave order. We discuss relevance of these results to recent and future experiments on volborthite.

The diffusion of clusters on a crystalline substrate submitted to a standing surface acoustic wave (StSAW) is studied using molecular dynamics simulations. The distributions of positions of clusters with two, three, and four atoms are calculated and evidence that the wave encourages the presence of the clusters in the vicinity of the maximum transverse displacement field of the substrate. The physical mechanism leading to this self-organization is expected to be equivalent to the one operating for a single adatom, i.e., the displacement of the clusters induced by the longitudinal displacement field of the wave. The detailed shapes of the distributions of positions of clusters are related to the different clusters' orientation and configurations. Finally, the possibility to use a StSAW to self-organize nanostructures during growth is addressed by simulating a deposition process on the substrate. We evidence that the use of a StSAW allows to especially control the spatial repartition of grown nanostructures.

Solid-state single-photon emitters (SPEs) are one of the prime components of many quantum nanophotonics devices. In this work, we report on an unusual, photoinduced blinking phenomenon of SPEs in gallium nitride. This is shown to be due to the modification in the transition kinetics of the emitter, via the introduction of additional laser-activated states. We investigate and characterize the blinking effect on the brightness of the source and the statistics of the emitted photons. Combining second-order correlation and fluorescence trajectory measurements, we determine the photodynamics of the trap states and characterize power-dependent decay rates and characteristic “off”-time blinking. Our work sheds light into understanding solid-state quantum system dynamics and, specifically, power-induced blinking phenomena in SPEs.

The interplay of competing orders is relevant to high-temperature superconductivity known to emerge upon suppression of a parent antiferromagnetic order typically via charge doping. How such interplay evolves at low temperature—in particular at what doping level the zero-temperature quantum critical point (QCP) is located—is still elusive because it is masked by the superconducting state. The QCP had long been believed to follow a smooth extrapolation of the characteristic temperature $T^{*}$ for the strange normal state well above the superconducting transition temperature. However, recently the $T^{*}$ within the superconducting dome was reported to unexpectedly exhibit back-bending likely in the cuprate ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$. Here we show that the original and revised phase diagrams can be understood in terms of weak and moderate competitions, respectively, between superconductivity and a pseudogap state such as $d$-density or spin-density wave, based on both Ginzburg-Landau theory and the realistic $t\text{−}{t}^{\prime }\text{−}{t}^{\prime \prime }\text{−}J\text{−}V$ model for the cuprates. We further found that the calculated temperature and doping-level dependence of the quasiparticle spectral gap and Raman response qualitatively agrees with the experiments. In particular, the $T^{*}$ back-bending can provide a simple explanation of the observed anomalous two-step thermal evolution dominated by the superconducting gap and the pseudogap, respectively. Our results imply that the revised phase diagram is likely to take place in high-temperature superconductors.

Conventionally, a basic requirement to generate valley Hall effect (VHE) is that the Berry curvature for conducting carriers in the momentum space be finite so as to generate anomalous deflections of the carriers originated from distinct valleys into different directions. We uncover a geometric valley Hall effect (gVHE) in which the valley-contrasting Berry curvature for carriers vanishes completely except for the singular points. The underlying physics is a singular non-$\pi$ fractional Berry flux located at each conical intersection point in the momentum space, analogous to the classic Aharonov-Bohm effect of a confined magnetic flux in real space. We demonstrate that, associated with gVHE, exceptional skew scattering of valley-contrasting quasiparticles from a valley-independent, scalar type of impurities can generate charge-neutral, transverse valley currents. As a result, the massless nature of the quasiparticles and their high mobility are retained. We further demonstrate that, for the particular Berry flux of $\pi /2$, gVHE is considerably enhanced about the skew scattering resonance, which is electrically controllable. A remarkable phenomenon of significant practical interest is that, associated with gVHE, highly efficient valley filtering can arise. These phenomena are robust against thermal fluctuations and disorders, making them promising for valleytronics applications.

We study the ground-state phase diagram of the Anderson-Hubbard model with correlated hopping at half-filling in one dimension. The Hamiltonian has a local Coulomb repulsion $U$ and a disorder potential with local energies randomly distributed in the interval $(-W,+W)$ with equal probability, acting on the singly occupied sites. The hopping process which modifies the number of doubly occupied sites is forbidden. The hopping between nearest-neighbor singly occupied and empty sites or between singly occupied and doubly occupied sites has the same amplitude $t$. We identify three different phases as functions of the disorder amplitude $W$ and Coulomb interaction strength $U>0$. When $U<4t$ the system shows a metallic phase: (i) only when no disorder is present $W=0$ or an Anderson-localized phase, (ii) when disorder is introduced $W\ne 0$. When $U>4t$ the Anderson-localized phase survives as long as disorder effects dominate on the interaction effects, otherwise a Mott-insulator phase (iii) arises. Phases (i) and (ii) are characterized by a finite density of doublons and a vanishing charge gap among the ground state and the excited states. Phase (iii) is characterized by the vanishing density of doublons and a finite gap for the charge excitations.

We use molecular dynamics to study the vibrations of a thermally fluctuating two-dimensional elastic membrane clamped at both ends. We directly extract the eigenmodes from resonant peaks in the frequency domain of the time-dependent height and measure the dependence of the corresponding eigenfrequencies on the microscopic bending rigidity of the membrane, taking care also of the subtle role of thermal contraction in generating a tension when the projected area is fixed. At finite temperatures we show that the effective (macroscopic) bending rigidity tends to a constant as the bare bending rigidity vanishes, consistent with theoretical arguments that the large-scale bending rigidity of the membrane arises from a strong thermal renormalization of the microscopic bending rigidity. Experimental realizations include covalently bonded two-dimensional atomically thin membranes such as graphene and molybdenum disulfide or soft matter systems such as the spectrin skeleton of red blood cells or diblock copolymers.

Dynamical quantum phase transitions (DQPTs) manifested in the nonanalyticities in the temporal evolution of a closed quantum system generated by the time-independent final Hamiltonian, following a quench (or ramping) of a parameter of the Hamiltonian, is an emerging frontier of nonequilibrium quantum dynamics. We, here, introduce the notion of a dynamical topological order parameter (DTOP) that characterizes these DQPTs occurring in quenched (or ramped) two-dimensional closed quantum systems; this is quite a nontrivial generalization of the notion of DTOP introduced in Budich and Heyl [Phys. Rev. B 93, 085416 (2016)] for one-dimensional situations. This DTOP is obtained from the “gauge-invariant” Pancharatnam phase extracted from the Loschmidt overlap, i.e., the modulus of the overlap between the initially prepared state and its time-evolved counterpart reached following a temporal evolution generated by the time-independent final Hamiltonian. This generic proposal is illustrated considering DQPTs occurring in the subsequent temporal evolution following a sudden quench of the staggered mass of the topological Haldane model on a hexagonal lattice where it stays fixed to zero or unity and makes a discontinuous jump between these two values at critical times at which DQPTs occur. What is remarkable is that while the topology of the equilibrium model is characterized by the Chern number, the emergent topology associated with the DQPTs is characterized by a generalized winding number.

We report a single-crystal neutron diffraction and inelastic neutron scattering study on the spin 1/2 cuprate ${\mathrm{Cu}}_3\mathrm{Bi}{\left({\mathrm{SeO}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$, complemented by dielectric and electric polarization measurements. The study clarifies a number of open issues concerning this complex material, whose frustrated interactions on a kagomelike lattice, combined with Dzyaloshinskii-Moriya interactions, are expected to stabilize an exotic canted antiferromagnetic order. In particular, we determine the nature of the structural transition occurring at 115 K, the magnetic structure below 25 K resolved in the updated space group, and the microscopic ingredients at the origin of this magnetic arrangement. This was achieved by an analysis of the measured gapped spin waves, which signifies the need for an unexpected and significant anisotropic exchange beyond the proposed Dzyaloshinskii-Moriya interactions. Finally, we discuss the multiferroic properties of this material with respect to the space group symmetries.

We investigate a superconducting interference device (SQUID) with two asymmetric Josephson junctions coupled to a mechanical resonator embedded in the loop of the SQUID. We quantize this system in the case when the frequency of the mechanical resonator is much lower than the cavity frequency of the SQUID and in the case when they are comparable. In the first case, the radiation pressure and the cross-Kerr type interactions arise and are modified by the asymmetry. The cross-Kerr type coupling is the leading term at the extremum points where the radiation pressure is zero. In the second case, the main interaction is the single-photon beam splitter, which exists only at a finite asymmetry. Another interaction in this regime is of cross-Kerr type, which exists at all asymmetries, but is generally much weaker than the beam splitter interaction. Increasing magnetic field can substantially enhance the optomechanical couplings strength with a potential for the radiation pressure coupling to reach the single-photon strong coupling regime, even the ultrastrong coupling regime, in which the single-photon coupling rate exceeds the mechanical frequency.