Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magnetoelectric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magnetoelectric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase shift ${\phi }_0$ in the current-phase relation. In particular we show that ${\phi }_0$ is proportional to the equilibrium spin current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magnetoelectric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.

The impact of the flexoelectric effect on the generalized susceptibility and soft phonon dispersion is not well known in the long-range-ordered phases of ferroics. Within the Landau-Ginzburg-Devonshire approach we obtained analytical expressions for the generalized susceptibility and phonon dispersion relations in the ferroelectric phase. The joint action of the static and dynamic flexoelectric effects induces nondiagonal components of the generalized susceptibility, whose amplitude is proportional to the convolution of the spontaneous polarization with the flexocoupling constants. The flexocoupling essentially broadens the $k$ spectrum of the generalized susceptibility and leads to an additional “pushing away” of the optical and acoustic soft mode phonon branches. The degeneracy of the transverse optical and acoustic modes disappears in the ferroelectric phase in comparison with the paraelectric phase due to the joint action of flexoelectric coupling and ferroelectric nonlinearity. The results obtained might be mainly important for theoretical analyses of a broad spectrum of experimental data, including neutron and Brillouin scattering.

The Majorana zero modes and persistent spin current in mesoscopic $d$-wave-superconducting loops with spin-orbit (SO) interaction are investigated by numerically solving the spin-generalized Bogoliubov–de Gennes equations self-consistently. For some appropriate strength of the SO coupling, Majorana zero-energy states and sharp jumps of the spin-polarized currents can be observed when the highest energy levels cross the Fermi energy in the spectrum, leading to spin currents with opposite chirality flowing near the inner and outer edges of the sample. When the threaded magnetic flux turns on, four flux-dependent patterns of the persistent spin current with step-like features show up, accompanied by Majorana edge modes at flux values where the energy gap closes. Moreover, the Majorana zero mode is highly influenced by the direction of the Zeeman field. A finite in-plane field can lead to the gap opening since the inversion symmetry is broken. Remarkably, multiple Majorana zero-energy states occur in the presence of an out-of-plane field ${\mathbf{h}}_z$, and the number of steps in the spin current evolution can be effectively tuned by the field strength due to the shift of Majorana zero modes. Finally, when the loop sample contains surface indentation defects, zero-energy modes can always show up in the presence of an appropriate ${\mathbf{h}}_z$. Interestingly, multiple Majorana states may be present in the system with a corner defect even if ${\mathbf{h}}_z=0$.

We analyze the critical behavior of the superfluid density ${\rho }_s$ in strongly disordered superconductors near the superconductor-insulator transition and compare it with the behavior of the spectral gap $\mathrm{\Delta }$ for collective excitations. We show that, in contrast to conventional superconductors, the superconductors with preformed pairs display an unusual scaling relation ${\rho }_s\propto {\mathrm{\Delta }}^2$ close to the superconductor-insulator transition. This relation has been reported in very recent experiments.

Topological Anderson transitions, which are direct phase transitions between topologically distinct Anderson localized phases, allow for criticality in one-dimensional disordered systems. We analyze the statistical properties of an ensemble of critical wave functions at such transitions. We find that the local moments are strongly inhomogeneous, with significant amplification towards the edges of the system. In particular, we obtain an analytic expression for the spatial profile of the local moments, which is valid at all topological Anderson transitions in one dimension, as we verify by direct comparison with numerical simulations of various lattice models.

We highlight the effect of structural hierarchy and deformation on band structure and wave-propagation behavior of two-dimensional phononic crystals. Our results show that the topological hierarchical architecture and instability-induced pattern transformations of the structure under compression can be effectively used to tune the band gaps and directionality of phononic crystals. The work provides insights into the role of structural organization and hierarchy in regulating the dynamic behavior of phononic crystals, and opportunities for developing tunable phononic devices.

We report direct lattice-level measurements of plastic relaxation kinetics through time-resolved, in situ Laue diffraction of shock-compressed single-crystal [001] Ta at pressures of 27–210 GPa. For a 50-GPa shock, a range of shear strains is observed extending up to the uniaxial limit for early data points ($<0.6$ ns), and the average shear strain relaxes to a near steady state over $\sim 1$ ns. For 80- and 125-GPa shocks, the measured shear strains are fully relaxed already at 200 ps, consistent with rapid relaxation associated with the predicted threshold for homogeneous nucleation of dislocations occurring at shock pressure $\sim 65$ GPa. The relaxation rate and shear stresses are used to estimate the dislocation density, and these quantities are compared to the results of other high-pressure work, flow stress models, and molecular dynamics simulations.

We study quenching dynamics of a one-dimensional transverse Ising chain with nearest neighbor antiferromagnetic interactions in the presence of a longitudinal field which renders the model nonintegrable. The dynamics of the spin chain is studied following a slow (characterized by a rate) or sudden quenches of the longitudinal field. Analyzing the temporal evolution of the Loschmidt overlap, we find different possibilities of the presence (or absence) of dynamical phase transitions (DPTs) manifested in the nonanalyticities of the rate function of the return probability. Even though the model is nonintegrable, there are periodic occurrences of DPTs when the system is slowly ramped across the quantum critical point (QCP) as opposed to the ferromagnetic version of the model; this numerical finding is qualitatively explained by mapping the original model to an effective integrable spin model which is appropriate for describing such slow quenches. Furthermore, concerning the sudden quenches, our numerical results show that in some cases, DPTs can be present even when the spin chain is quenched within the same phase or even to the QCP, while in some other situations they completely disappear even after quenching across the QCP. These observations lead us to the conclusion that it is the change in the nature of the ground state that determines the presence of DPTs following a sudden quench.

The effect of Cr substitution in a $\mathrm{SrRu}{\mathrm{O}}_3$ epitaxial thin film on $\mathrm{SrTi}{\mathrm{O}}_3$ substrate was investigated by measuring the magnetic and transport properties and the electronic states. The ferromagnetic transition temperature of the $\mathrm{SrR}{\mathrm{u}}_{0.9}\mathrm{C}{\mathrm{r}}_{0.1}{\mathrm{O}}_3$ film (166 K) was higher than that of the $\mathrm{SrRu}{\mathrm{O}}_3$ film (147 K). Resonant photoemission spectroscopy experimentally revealed that the $\mathrm{Cr}3d{t}_{2g}$ orbital is hybridized with the $\mathrm{Ru}4d{t}_{2g}$ orbital in the $\mathrm{SrR}{\mathrm{u}}_{0.9}\mathrm{C}{\mathrm{r}}_{0.1}{\mathrm{O}}_3$ film, supporting the assumption that the enhancement of the ferromagnetic transition temperature through Cr substitution stems from the widening of energy bands due to the hybridization of $\mathrm{Cr}3d{t}_{2g}$ and $\mathrm{Ru}4d{t}_{2g}$ orbitals. Furthermore, we found that the Hall resistivity of the $\mathrm{SrR}{\mathrm{u}}_{0.9}\mathrm{C}{\mathrm{r}}_{0.1}{\mathrm{O}}_3$ film at low temperature is not a linear function of magnetic field in the high-field region where the out-of-plane magnetization was saturated; this result suggests that the $\mathrm{SrR}{\mathrm{u}}_{0.9}\mathrm{C}{\mathrm{r}}_{0.1}{\mathrm{O}}_3$ film undergoes a structural transition at low temperature accompanied with the modulation of the Fermi surface.

We demonstrate theoretically and experimentally that four-wave mixing processes obey phase-matching conditions that determine not only the conservation of the photon energy and k-momentum but also the orbital angular momentum of light. We report on time-resolved four-wave mixing experiments performed on a CdTe/CdZnTe quantum well in both noncollinear and collinear configurations with Laguerre-Gauss beams. They demonstrate that the polarization wave which is induced in the material keeps memory of the excitation pulse orbital momentum. We show that in the collinear configuration, the large angular acceptance opens up new horizons for improving the spatial resolution in time-resolved experiments.

Tunnel coupling between two dots in manganese-doped InAs/GaAs quantum dot molecules (QDMs), valence band mixing, and $p-d$ exchange interaction between holes and localized $d$ electrons give rise to a tunability of charge, spin, and molecular orbitals. The interplay among them determines the nature of the molecular ground state. Remarkably, unlike usual diatomic molecules in which the bonding (BD) state is always the ground state, we found that the molecular ground state in Mn-doped QDMs is of antibonding (AB) character. Furthermore, it is a spin-split state and can be switched into the spin-split BD type. We also demonstrate that this unusual behavior can be tuned by the lateral confinement strength of the QDMs, the concentration, and the distribution of manganese as well as the electric field applied along the direction of the QDM axis.

We study bosonic and fermionic quantum two-leg ladders with orbital magnetic flux. In such systems, the ratio $\nu$ of particle density to magnetic flux shapes the phase space, as in quantum Hall effects. In fermionic (bosonic) ladders, when $\nu$ equals one over an odd (even) integer, Laughlin fractional quantum Hall (FQH) states are stabilized for sufficiently long-ranged repulsive interactions. As a signature of these fractional states, we find a unique dependence of the chiral currents on particle density and on magnetic flux. This dependence is characterized by the fractional filling factor $\nu$, and forms a stringent test for the realization of FQH states in ladders, using either numerical simulations or future ultracold-atom experiments. The two-leg model is equivalent to a single spinful chain with spin-orbit interactions and a Zeeman magnetic field, and results can thus be directly borrowed from one model to the other.

We study the electronic transport in an infinite one-dimensional Hubbard chain, driven by a homogeneous electric field. The physical chain is coupled to fermionic bath chains in order to account for dissipation and to prevent the occurrence of Bloch oscillations. The steady-state current is computed in the frame of Keldysh Green's functions in cluster perturbation theory. The current characteristics are dominated by resonant-tunneling-like structures, which can be traced back to Wannier-Stark resonances due to antiferromagnetic correlations. The same current characteristic occurs in a noninteracting Wannier-Stark model with alternating on-site energies. Nonlocal effects of the self-energy can be accounted for the observed physical behavior.

We propose a simple mean-field ansatz to study phase transitions from a topological phase to a trivial phase. We probe the efficiency of this approach by considering the string-net model in the presence of a string tension for any anyon theory. Such a perturbation is known to be responsible for a deconfinement-confinement phase transition which is well described by the present variational setup. We argue that mean-field results become exact in the limit of large total quantum dimension.

The nature of multipolar order and hyperfine-enhanced (HE) ${}^{141}\mathrm{Pr}$ nuclear spin dynamics in ${\mathrm{PrV}}_2{\mathrm{Al}}_{20}$ was investigated using the muon spin relaxation technique. No explicit sign of time-reversal symmetry breaking was found below the multipolar order temperature $T_Q\sim 0.6$ K in a zero applied field as anticipated on the basis of the antiferroquadrupolar (AFQ) order picture proposed by Sakai and Nakatsuji [J. Phys. Soc. Jpn. 80, 063701 (2011)]. Further evidence of the nonmagnetic ground state was obtained from the observation of HE ${}^{141}\mathrm{Pr}$ nuclear spin fluctuations in the MHz scale. A marked increase in the muon spin-lattice relaxation rate ($1/T_{1,\mu }$) was observed below 1 K with decreasing temperature, which was attributed to the perturbation on the HE ${}^{141}\mathrm{Pr}$ nuclear spin dynamics associated with the development of AFQ correlations. The longitudinal field dependence of $1/T_{1,\mu }$ revealed that the enhanced ${}^{141}\mathrm{Pr}$ nuclear spin accidentally has an effective gyromagnetic ratio close to that of the muon.

Here, we present a detailed study on the temperature and angular dependence of the Shubnikov–de Haas (SdH) effect in the semimetal ${\mathrm{WTe}}_2$. This compound was recently shown to display a very large nonsaturating magnetoresistance which was attributed to nearly perfectly compensated densities of electrons and holes. We observe four fundamental SdH frequencies and attribute them to spin-orbit split, electron-like, and hole-like Fermi-surface (FS) cross-sectional areas. Their angular dependence seems consistent with ellipsoidal FSs with volumes suggesting a modest excess in the density of electrons with respect to that of the holes. We show that density functional theory (DFT) calculations fail to correctly describe the FSs of ${\mathrm{WTe}}_2$. When their cross-sectional areas are adjusted to reflect the experimental data, the resulting volumes of the electron/hole FSs obtained from the DFT calculations would imply a pronounced imbalance between the densities of electrons and holes. We find evidence for field-dependent Fermi-surface cross-sectional areas by fitting the oscillatory component superimposed onto the magnetoresistivity signal to several Lifshitz-Kosevich components. We also observe a pronounced field-induced renormalization of the effective masses. Taken together, our observations suggest that the electronic structure of ${\mathrm{WTe}}_2$ evolves with the magnetic field due to the Zeeman splitting. This evolution is likely to contribute to its pronounced magnetoresistivity.

Unidirectional and robust transport is generally observed at the edge of two- or three-dimensional quantum Hall and topological insulator systems. A hallmark of these systems is topological protection, i.e., the existence of propagative edge states that cannot be scattered by imperfections or disorder in the system. A different and less explored form of robust transport arises in non-Hermitian systems in the presence of an imaginary gauge field. As compared to topologically protected transport in quantum Hall and topological insulator systems, robust non-Hermitian transport can be observed in lower dimensional (i.e., one dimensional) systems. In this work the transport properties of one-dimensional tight-binding lattices with an imaginary gauge field are theoretically investigated, and the physical mechanism underlying robust one-way transport is highlighted. Back scattering is here forbidden because reflected waves are evanescent rather than propagative. Remarkably, the spectral transmission of the non-Hermitian lattice is shown to be mapped onto the one of the corresponding Hermitian lattice, i.e., without the gauge field, but computed in the complex plane. In particular, at large values of the gauge field the spectral transmittance becomes equal to 1, even in the presence of disorder or lattice imperfections. This phenomenon can be referred to as one-way non-Hermitian transparency. Robust one-way transport can be also realized in a more realistic setting, namely in heterostructure systems, in which a non-Hermitian disordered lattice is embedded between two homogeneous Hermitian lattices. Such a double heterostructure realizes asymmetric (nonreciprocal) wave transmission. A physical implementation of non-Hermitian transparency, based on light transport in a chain of optical microring resonators, is suggested.

The operation speed of thermoelectric devices is generally limited to microsecond or millisecond time scales. This is due to the difficulty in manipulating and measuring the thermoelectric transients at high speeds. Although recent advances in optical characterization techniques have succeeded to detect thermoelectric signals in picosecond time scales in a few special nanomaterials such as graphene, thermoelectric dynamics in most of the standard thermoelectric materials still remain unknown. Here we investigate the picosecond carrier dynamics of standard thermoelectric ${\mathrm{Ca}}_x{\mathrm{CoO}}_2$ thin films by means of terahertz emission spectroscopy. The terahertz radiation signals generated from the ${\mathrm{Ca}}_x{\mathrm{CoO}}_2$ films by femtosecond laser absorption are found to be strongly dependent on crystal orientation. We discuss that the terahertz emission properties of ${\mathrm{Ca}}_x{\mathrm{CoO}}_2$ films can be described well in terms of the unique tensorial properties of the Seebeck coefficient. The unordinary terahertz emission property associated with the tensorial property of a Seebeck coefficient provides convincing evidence of picosecond evolution of the thermoelectric current even in this standard material. Our results not only promote general understanding of the ultrafast charge dynamics in solids but may also pave the way to develop optoelectronic devices including bias-free terahertz sources and high-speed infrared sensors.

We develop a theory of magnetic circular dichroism (MCD) of hard x-ray Raman scattering (XRS) to analyze the MCD signal at iron $L$ edge from pure ferromagnetic iron. The obtained formula of scattering amplitude has terms corresponding to the charge (Thomson) scattering process, and the orbital and spin scattering processes in the elastic x-ray magnetic scattering. The total scattering intensity is almost independent of incident photon helicity since it is mainly produced by the charge scattering. The weak MCD signals are caused primarily by interference between the charge scattering amplitude and each of the orbital and spin scattering amplitudes. The shape of the MCD spectra depends on angle ${\alpha }_{\mathrm{M}}$ between the wave vector of the incident photon and the magnetization vector. At ${\alpha }_{\mathrm{M}}=0^{\circ }$, the spin scattering is suppressed so that the MCD spectrum becomes analogous to that observed in the x-ray absorption spectroscopy. At ${\alpha }_{\mathrm{M}}={135}^{\circ }$, the orbital scattering is suppressed, and the spin scattering plays central roles in producing the MCD signal. The magnitude of the MCD signal turns out to be proportional to the spin density of states projected onto the $3d$ states in the unoccupied state. Consequently, the value of the integrated MCD signal is proportional to the spin moment in the $3d$ states at the scattering site. The calculated MCD spectra with the help of a band structure calculation well reproduce the observed spectra.