Dynamics of topological magnetic textures are typically induced externally by, e.g., magnetic fields or spin/charge currents. Here, we demonstrate the effect of the internal-to-the-system geometry-induced motion of a domain wall in a curved nanostripe. Being driven by a gradient of the curvature of a stripe with biaxial anisotropy, transversal domain walls acquire remarkably high velocities of up to $100\mathrm{m}/\mathrm{s}$ and do not exhibit any Walker-type speed limit. We pinpoint that the inhomogeneous distribution of the curvature-induced Dzyaloshinskii-Moriya interaction is a driving force for the motion of a domain wall. Although we showcase our approach on the specific Euler spiral geometry, the approach is general and can be applied to a wide class of geometries.

Spin-to-charge current interconversions are widely exploited for the generation and detection of pure spin currents and are key ingredients for future spintronic devices including spin-orbit torques and spin-orbit logic circuits. In the case of the spin Hall effect, different mechanisms contribute to the phenomenon and determining the leading contribution is peremptory for achieving the largest conversion efficiencies. Here, we experimentally demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in highly resistive Ta. We obtain an intrinsic spin Hall conductivity for β-Ta of $-820\pm 120(\hslash /e){\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$ from spin absorption experiments in a large set of lateral spin valve devices. The predominance of the intrinsic mechanism in Ta allows us to linearly enhance the spin Hall angle by tuning the resistivity of Ta, reaching up to −35 ± 3%, the largest reported value for a pure metal.

The effects of dilution disorder and random-displacement disorder are analyzed for dipolar-coupled magnetic moments confined in a plane, which were originally placed on the square lattice. In order to distinguish the different phases, new order parameters are derived and parallel tempering Monte Carlo simulations are performed for a truncated dipolar Hamiltonian to obtain the phase diagrams for both types of disorder. We find that both dilution disorder and random-displacement disorder give similar phase diagrams, namely, disorder at small enough temperatures favors a so-called microvortex phase. This can be understood in terms of the flux closure present in dipolar-coupled systems.

The structural or electronic symmetry breaking of the host lattice is a recurrent phenomenon in many quantum materials, including superconductors. Yet, how these broken-symmetry states affect the electronic pair wave function of superconductivity has been rarely elucidated. Here, using low-temperature scanning-tunneling microscopy and first-principles calculations, we identify the broken rotational symmetry via stripe ordering on the (001) surface of perovskite ${\mathrm{BaBi}}_3$ films grown by molecular-beam epitaxy, and show that it consequently leads to anisotropic superconductivity with twofold symmetry. In contrast, the structural disorder smears out the anisotropy of electron pairing and fills superconducting subgap density of states as the film thickness is reduced. A quasi-long-range model of superconducting fluctuations is revealed to describe the tunneling conductance spectra of thin ${\mathrm{BaBi}}_3$ films well, and to exemplify how disorders contribute to the low-energy quasiparticle excitations in superconductors. Our findings help understand the effects of symmetry-breaking states and disorders on superconductivity, particularly the existing tunneling conductance spectra there.

We identify ground states of one-dimensional fermionic systems subject to competing repulsive interactions of finite range, and provide phenomenological and fundamental signatures of these phases and their transitions. Commensurable particle densities admit multiple competing charge-ordered insulating states with various periodicities and internal structure. Our reference point are systems with interaction range $p=2$, where phase transitions between these charge-ordered configurations are known to be mediated by liquid and bond-ordered phases. For increased interaction range $p=4$, we find that the phase transitions can also appear to be abrupt, as well as being mediated by re-emergent ordered phases that cross over into liquid behavior. These considerations are underpinned by a classification of the competing charge-ordered states in the atomic limit for varying interaction range at the principal commensurable particle densities. We also consider the effects of disorder, leading to fragmentization of the ordered phases and localization of the liquid phases.

We study energy transport in the integrable ${\mathbb{Z}}_3$ parafermionic chain using the partitioning protocol. By exploiting the Bethe-ansatz solution for the thermodynamics of the system, we develop a generalized hydrodynamic description of the nonequilibrium steady states, which we benchmark using numerical simulations based on matrix product states. The model features a low-energy conformal limit with central charge $c=\frac{4}{5}$, which affects the low-temperature energy current, as we explicitly show. Moreover, we exploit that, for energies close to the maximally excited state, the system is also critical and described by a conformal field theory with $c=1$. By considering the two halves prepared at two temperatures both low in value but opposite in sign, we are able to investigate in an exact and controlled way the junction between two conformal field theories with different central charges. Notwithstanding the absence of global conformal invariance, we find results that approximate to a high degree those of out-of-equilibrium conformal field theories. Our study extends the generalized hydrodynamics to a framework where it can be profitably used for exploring new physical phenomena.

We consider an $\alpha -T_3$ lattice illuminated by intense circularly polarized radiation in the terahertz regime. We present the quasienergy band structure, time-averaged energy spectrum, and time-averaged density of states of an $\alpha -T_3$ lattice by solving the Floquet Hamiltonian numerically. We obtain exact analytical expressions of the quasienergies at the Dirac points for all values of $\alpha$ and field strength. We find that the quasienergy band gaps at the Dirac point decrease with increase of $\alpha$. Approximate forms of quasienergy and band gaps at single- and multiphoton resonant points are derived using the rotating wave approximation. The expressions reveal a stark dependence of quasienergy on the Berry phase of the charge carrier. The quasienergy flat band remains unaltered in the presence of radiation for a dice lattice ($\alpha =1$). However, it acquires a dispersion in and around the Dirac and even-photon resonant points when $0<\alpha <1$. The valley degeneracy and electron-hole symmetry in the quasienergy spectrum are broken for $0<\alpha <1$. Unlike graphene, the mean energy closely follows the linear dispersion of the Dirac cones until near the single-photon resonant point in the dice lattice. There are additional peaks in the time-averaged density of states at the Dirac point for $0<\alpha \le 1$.

We present a proof-of-principle of how electronic transport measurements permit the observation of the Autler-Townes doublet, an optical property of nanodevices. The quantum physical system consists of one optically pumped quantum dot, a second auxiliary quantum dot, and a superconductor lead, which provides an effective coupling between the dots via crossed Andreev reflection. Electrodes, working as sources or drains, act as nonequilibrium electronic reservoirs. Our calculations of the photocurrent at both transient and stationary regimes, obtained using a density matrix formalism for open quantum systems, shows signatures of the formation of the Autler-Townes doublet, caused by the interplay between the optical pumping and the crossed Andreev reflection.

We describe a general method to identify exact, local parent Hamiltonians for trial states such as quantum Hall or spin-liquid states, which we have used extensively during the past decade. It can be used to identify exact parent Hamiltonians, either directly or via the construction of simpler annihilation operators from which a parent Hamiltonian respecting all the required symmetries can be constructed. Most remarkably, however, the method provides approximate parent Hamiltonians whenever an exact solution is not available within the space of presumed interaction terms.

Negative longitudinal and positive in-plane transverse magnetoresistance have been observed in most topological Dirac/Weyl semimetals and some other topological materials. Here, we present a quantum theory of intrinsic magnetoresistance for three-dimensional Dirac fermions at a finite and uniform magnetic field $B$. In a semiclassical regime, it is shown that the longitudinal magnetoresistance is negative and quadratic of a weak field $B$ while the in-plane transverse magnetoresistance is positive and quadratic of $B$. The relative magnetoresistance is inversely quartic of the Fermi wave vector and only determined by carrier density, irrelevant to the external scatterings in the weak scattering limit. This intrinsic anisotropic magnetoresistance is measurable in systems with low carrier density and high mobility. In the quantum oscillation regime a formula for the phase shift in Shubnikov–de Haas oscillation is present as a function of the mobility and the magnetic field, which is helpful for experimental data analysis.

The dependence of excited-state properties on dimensionality is the most prominent character of nanostructures. Using first-principles many-body perturbation theory, we show how those excited-state properties, i.e., quasiparticle energies and excitons, evolve with the dimensionality of tellurium nanostructures that have attracted significant interest because of their high carrier mobility and air stability. Even though the elementary atomistic structures are similar, dimensionality dictates many-electron interactions and excited-state properties: the self-energy correction to the band gap is increased from 0.22 eV in bulk to 0.90 eV in a two-dimensional (2D) monolayer, and ultimately to 2.70 eV in a one-dimensional (1D) spiral tube; excitonic effects are weak in bulk with an exciton binding energy less than 10 meV, while the exciton binding energy is substantially enhanced to be 0.67 eV in the monolayer and 2.40 eV in the 1D structure. Interestingly, reduced dimensionality also produces substantial anisotropic optical response through many-electron interactions: local-field effects dominate the optical spectra of 2D and 1D structures and induce highly anisotropic optical responses. These results not only reveal a systematic picture for understanding the evolution of excited-state properties with dimensionality but also suggest the possibility of designing macroscopic electronic and optical properties by engineering nanosized building blocks.

Within the real space renormalization group we obtain the phase portrait of the anisotropic quantum $XY$ model on square lattice in presence of Dzyaloshinskii-Moriya (DM) interaction. The model is characterized by two parameters, $\lambda$ corresponding to $XY$ anisotropy, and $D$ corresponding to the strength of DM interaction. The flow portrait of the model is governed by two global Ising-Kitaev attractors at $(\lambda =\pm 1,D=0)$ and a repeller line, $\lambda =0$. This line itself is characterized by an attractor at $D=0$. Renormalization flow of concurrence suggests that the $\lambda =0$ line corresponds to a topological phase transition. The gap starts at zero on this repeller line corresponding to superfluid phase of underlying bosons; and flows towards a finite value at the Ising-Kitaev points. At these two fixed points the spin fields become purely classical, and hence the resulting Ising degeneracy can be interpreted as topological degeneracy of dual degrees of freedom. The state of affairs at the Ising-Kitaev fixed point is consistent with the picture of a $p$-wave pairing of strength $\lambda$ of Jordan-Wigner fermions coupled with Chern-Simons gauge fields.

In nonmagnetic insulators, phonons are the carriers of heat. If heat enters in a region and temperature is measured at a point within phonon mean free paths of the heated region, ballistic propagation causes a nonlocal relation between local temperature and heat insertion. This paper focuses on the solution of the exact Peierls-Boltzmann equation (PBE), the relaxation time approximation (RTA), and the definition of local temperature needed in both cases. The concept of a nonlocal “thermal susceptibility” (analogous to charge susceptibility) is defined. A formal solution is obtained for heating with a single Fourier component $P(\vec{r},t)=P_{0}exp(i\vec{k}·\vec{r}-i\omega t)$, where $P$ is the local rate of heating). The results are illustrated by Debye model calculations in RTA for a three-dimensional periodic system where heat is added and removed with $P(\vec{r},t)=P\left(x\right)$ from isolated evenly spaced segments with period $L$ in $x$. The ratio $L/{\ell }_{\min }$ is varied from 6 to $\infty$, where ${\ell }_{\min }$ is the minimum mean free path. The Debye phonons are assumed to scatter anharmonically with mean free paths varying as ${\ell }_{\min }{(q_D/q)}^2$ where $q_D$ is the Debye wave vector. The results illustrate the expected local (diffusive) response for ${\ell }_{\min }\ll L$, and a diffusive to ballistic crossover as ${\ell }_{\min }$ increases toward the scale $L$. The results also illustrate the confusing problem of temperature definition. This confusion is not present in the exact treatment but occurs in RTA.

This paper reports on the temporal and spectral light field evolution for two different types of metallic gratings after illumination with a near-infrared TM-polarized femtosecond pulse: a freestanding grating in air and a grating on a dielectric substrate. The electromagnetic field components are calculated numerically at various transverse locations of the gratings by use of a finite-difference time-domain model. The spectral dynamics are explained by the dynamics of surface plasmon polaritons (SPPs). Fano-like profiles are observed close to an SPP resonance in the calculated spectral curves, indicating a connection between the Rayleigh anomaly and a nearby SPP resonance. For the freestanding grating, only a single Fano-like profile close to the air/metal SPP resonance and, with the dielectric support, two Fano-type profiles are observed, one in the proximity of the air/metal SPP resonance, the other in the proximity of the substrate/metal resonance. Investigating the changes in the spectra for an increasing distance to the grating, it is found that with increasing distance, the spectral curves related to different transverse locations coincide almost completely, providing evidence that the near-field contributions disappeared.

Antiferroelectric ultrathin ${\mathrm{PbZrO}}_3$ films can exhibit both ferroelectric and antiferroelectric behavior depending on the thickness. We use first-principles-based nanoscopic simulations to investigate the intrinsic high-frequency dynamics of the electric-field-induced phase switching in such films which so far remains unknown. In this comprehensive study we report (i) the size and frequency evolution of the polarization response to the electric field; (ii) the intrinsic time for the phase switching; (iii) detailed comparison between the polarization reversal in the films with ferroelectric and antiferroelectric behavior; (iv) dynamics of the antiferroelectric and antiferrodistortive order parameters; (v) nanoscopic mechanism responsible for the phase switching. The nanoscopic insight leads to the prediction of the existence of two possible scenarios for the antipolar-polar phase switching depending on the mutual orientation of the antiferroelectric order parameter and the electric field. The two scenarios have different dynamical fingerprints. The polar-antipolar phase switching is found to be assisted by the formation of a nonpolar phase. Computational data indicate that the phase switching time is only fractions of nanoseconds for the polar-polar phase switching in ferroelectric films and polar-antipolar phase switching in antiferroelectric films. The antipolar-polar phase switching in antiferroelectric films is just a bit slower and takes the order of nanosecond. Under nonequilibrium conditions we find formation of antiferroelectric and antiferrodistortive nanodomains and coexistence of polar and antipolar order parameters.

We demonstrate that a combination of disorder and interactions in a two-dimensional bulk topological insulator can generically drive its helical edge insulating. We establish this within the framework of helical Luttinger liquid theory and exact Emery-Luther mapping. The gapless glassy edge state spontaneously breaks time-reversal symmetry in a “spin glass” fashion, and may be viewed as a localized state of solitons, which carry half-integer charge. Such a qualitatively distinct edge state provides a simple explanation for heretofore puzzling experimental observations. This phase exhibits a striking nonmonotonicity, with the edge growing less localized in both the weak and strong disorder limits.

Magnetic exchange in Kondo lattice systems is of the Ruderman-Kittel-Kasuya-Yosida type, whose sign depends on the Fermi wave vector $k_F$. In the simplest setting, for small $k_F$, the interaction is predominately ferromagnetic, whereas it turns more antiferromagnetic with growing $k_F$. It is remarkable that even though $k_F$ varies vastly among the rare-earth systems, an overwhelming majority of lanthanide magnets are in fact antiferromagnets. To address this puzzle, we investigate the effects of a $p$-wave form factor for the Kondo coupling pertinent to nearly all rare-earth intermetallics. We show that this leads to interference effects which for small $k_F$ are destructive, greatly reducing the size of the RKKY interaction in the cases where ferromagnetism would otherwise be strongest. By contrast, for large $k_F$, constructive interference can enhance antiferromagnetic exchange. Based on this, we propose a route for designing ferromagnetic rare-earth magnets.

Averievite, ${\mathrm{Cu}}_5{\mathrm{V}}_2{\mathrm{O}}_{10}\left(\mathrm{CsCl}\right)$, is an oxide mineral composed of ${\mathrm{Cu}}^{2+}$ kagome layers sandwiched by ${\mathrm{Cu}}^{2+}\text{−}{\mathrm{V}}^{5+}$ honeycomb layers. We have synthesized this oxide and investigated its properties from ab initio calculations along with susceptibility and specific heat measurements. The data indicate a Curie-Weiss temperature of 185 K as well as long-range magnetic order at 24 K due to the significant interlayer coupling from the honeycomb copper ions. This order is suppressed by substituting copper by isoelectronic zinc, suggesting that Zn-substituted averievite is a promising spin liquid candidate. A further proposed substitution that replaces ${\mathrm{V}}^{5+}$ by ${\mathrm{Ti}}^{4+}$ not only dopes the material but is predicted to give rise to a two-dimensional electronic structure featuring Dirac crossings. As such, averievite is an attractive platform for $S=1/2$ kagome physics with the potential for realizing novel electronic states.

We study coherent quantum phase slips in a Josephson junction chain, including two types of quenched disorder: random spatial modulation of the junction areas and random induced background charges. Usually, the quantum phase-slip amplitude is sensitive to the normal-mode structure of superconducting phase oscillations in the ring (Mooij-Schön modes, which are all localized by the area disorder). However, we show that the modes' contribution to the disorder-induced phase-slip action fluctuations is small, and the fluctuations of the action on different junctions are mainly determined by the local junction parameters. We study the statistics of the total quantum phase-slip amplitude on the chain and show that it can be non-Gaussian for not sufficiently long chains.