We investigate electrical transport in a three-dimensional massless Dirac fermion model that describes a Dirac semimetal state realized in topological materials. We derive a set of interdependent diffusion equations with eight local degrees of freedom, including the electric charge density and the spin density, that respond to an external electric field. By solving the diffusion equations for a system with a boundary, we demonstrate that a spin Hall effect with spin accumulation occurs even though the conventional spin current operator is zero. The Noether current associated with chiral symmetry, known as the axial current, is also discussed. We demonstrate that the axial current flows near the boundary and that it is perpendicular to the electric current.

The Doppler effect is a fundamental physical phenomenon observed for waves propagating in vacuum or various media, commonly gaseous or liquid. Here, we report on the occurrence of a Doppler effect in a solid medium. Instead of a real object, a topological soliton, i.e., a magnetic domain wall (DW) traveling in a current-carrying ferromagnetic nanowire, plays the role of the moving wave source. The Larmor precession of the DW in an external field stimulates emission of monochromatic spin waves (SWs) during its motion, which show a significant Doppler effect, comparable to the acoustic one of a train whistle. This process involves two prominent spin-transfer-torque effects simultaneously, the current-driven DW motion and the current-induced SW Doppler shift. The latter gives rise to an interesting feature, i.e., the observed SW Doppler effect appears resulting from a stationary source and a moving observer, contrary to the laboratory frame.

High-resolution single crystal neutron diffraction measurements are presented probing the magnetostructural response to uniaxial pressure in the iron pnictide parent system ${\mathrm{BaFe}}_2{\mathrm{As}}_2$. Scattering data reveal a strain-activated, anisotropic broadening of nuclear Bragg reflections, which increase upon cooling below the resolvable onset of global orthorhombicity. This anisotropy in lattice coherence continues to build until a lower temperature scale—the first-order onset of antiferromagnetism—is reached. Our data suggest that antiferromagnetism and strong magnetoelastic coupling drive the strain-activated lattice response in this material and that the development of anisotropic lattice correlation lengths under strain is a possible origin for the high temperature transport anisotropy in this compound.

High-pressure solid-state transformations at high strain rates are usually observed after the fact, either during static holding or after unloading, or inferred from interferometry measurements of the sample surface. The emergence of femtosecond x-ray diffraction techniques provides insight into the dynamics of short-time-scale events such as shocks. We report laser pump-probe experiments of the response of Zr to laser-driven shocks over the first few nanoseconds of the shock event, enabling the $\alpha \to \omega$ transition and orientation relationship to be observed in real time with picosecond resolution. A clear orientation relationship of ${\left(10\overline{1}0\right)}_{\alpha }\left|\right|{\left(10\overline{1}1\right)}_{\omega }$ is found, in conflict with $\omega \to \alpha$ annealing experiments in zirconium and the two $\alpha \to \omega$ pathways proposed for titanium.

Grimme's DFT-D dispersion contribution to interatomic forces constants, required for the computation of the phonon band structures in density-functional perturbation theory, has been derived analytically. The implementation has then been validated with respect to frozen phonons, and applied on materials where weak cohesive forces play a major role, i.e., argon, graphite, benzene, etc. We show that these dispersive contributions have to be considered to properly reproduce the experimental vibrational properties of these materials, although the lattice parameter change, coming from the ground-state relaxation with the proper functional, induces the most important change with respect to a treatment without dispersion corrections. In the current implementation, the contribution of these dispersion corrections to the dynamical matrices (with a number of elements that is proportional to the square of the number of atoms) has only a cubic scaling with the number of atoms. In practice, the overload with respect to density-functional calculations is small, making this methodology promising to study vibrational properties of large dispersive systems.

We study the density of states (DOS) in diffusive superconductors with pointlike magnetic impurities of arbitrary strength described by the Poissonian statistics. The mean-field theory predicts a nontrivial structure of the DOS with the continuum of quasiparticle states and (possibly) the impurity band. In this approximation, all the spectral edges are hard, marking distinct boundaries between spectral regions of finite and zero DOS. Considering instantons in the replica sigma-model technique, we calculate the average DOS beyond the mean-field level and determine the smearing of the spectral edges due interplay of fluctuations of potential and nonpotential disorder. The latter, represented by inhomogeneity in the concentration of magnetic impurities, affects the subgap DOS in two ways: via fluctuations of the pair-breaking strength and via induced fluctuations of the order parameter. In limiting cases, we reproduce previously reported results for the subgap DOS in disordered superconductors with strong magnetic impurities.

The evolution of the spin transition in ${\mathrm{LaCoO}}_3$ has been investigated with photoemission electron microscopy (PEEM) as a function of temperature. The investigated temperature range spanned from a predominantly low spin configuration (125 K) to the proposed percolation limit for metallization (413 K). The data show that the spin configuration exhibits an inhomogeneous spatial distribution that is very sensitive to the surface preparation method. In the region of the semiconductor-to-metal transition (300 to 450 K), the spatial contrast is continuously reduced, indicating a smooth transition without domain percolation. These observations support a new interpretation of the temperature evolution of the system that is in agreement with current theoretical understanding of the spin transition.

A set of scalar operators, originally introduced in connection with an analytic first-Landau-level (FLL) construction of fractional quantum Hall (FQHE) wave functions for the sphere, are employed in a somewhat different way to generate explicit representations of both hierarchy states (e.g., the series of fillings $\nu =1/3$, 2/5, 3/7,$\cdots$) and their conjugates ($\nu =1$, 2/3, 3/5,$\cdots$) as noninteracting quasielectrons filling fine-structure subshells within the FLL. This yields, for planar and spherical geometries, a quasielectron representation of the incompressible FLL state of filling $p/(2p+1)$ in a magnetic field of strength B that is algebraically identical to the IQHE state of filling $\nu =p$ in a magnetic field of strength $\mathrm{B}/(2p+1)$. The construction provides a precise definition of the quasielectron/composite fermion that differs in some respects from common descriptions: they are eigenstates of $L,L_z$; they and the FLL subshells they occupy carry a third index $\mathcal{I}$ that is associated with breaking of scalar pairs; they absorb in their internal wave functions one, not two, units of magnetic flux; and they share a common, simple structure as vector products of a spinor creating an electron and one creating magnetic flux. We argue that these properties are a consequence of the breaking of the degeneracy of noninteracting electrons within the FLL by the scale-invariant Coulomb potential. We discuss the sense in which the wave function construction supports basic ideas of both composite fermion and hierarchical descriptions of the FQHE. We describe symmetries of the quasielectrons in the $\nu =1/2$ limit, where a deep Fermi sea of quasielectrons forms, and the quasielectrons take on Majorana and pseudo-Dirac characters. Finally, we show that the wave functions can be viewed as fermionic excitations of the bosonic half-filled shell, producing at $\nu =1/2$ an operator that differs from but plays the same role as the Pfaffian.

Anyons exist as pointlike particles in two dimensions and carry braid statistics, which enable interactions that are independent of the distance between the particles. Except for a relatively few number of models, which are analytically tractable, much of the physics of anyons remains still unexplored. In this paper, we show how U(1) symmetry can be combined with the previously proposed anyonic matrix product states to simulate ground states and dynamics of anyonic systems on a lattice at any rational particle number density. We provide proof of principle by studying itinerant anyons on a one-dimensional chain where no natural notion of braiding arises and also on a two-leg ladder where the anyons hop between sites and possibly braid. We compare the result of the ground-state energies of Fibonacci anyons against hardcore bosons and spinless fermions. In addition, we report the entanglement entropies of the ground states of interacting Fibonacci anyons on a fully filled two-leg ladder at different interaction strength, identifying gapped or gapless points in the parameter space. As an outlook, our approach can also prove useful in studying the time dynamics of a finite number of non-Abelian anyons on a finite two-dimensional lattice.

We establish a variational principle for properly mapping a fractional quantum Hall state to a fractional Chern insulator (FCI). We find that the mapping has a gauge freedom which could generate a class of FCI ground-state wave functions appropriate for different forms of interactions. Therefore, the gauge should be fixed by a variational principle that minimizes the interaction energy of the FCI model. For a soft and isotropic electron-electron interaction, the principle leads to a gauge coinciding with that for maximally localized two-dimensional projected Wannier functions of a Landau level.

Integrability of electron dynamics in one dimension is manifested by the nonequilibrium stationary states. They emerge near a point contact coupling two quantum Hall edges with different chemical potentials. I use the nonequilibrium bosonization technique to show that the effective temperature of such states at the fractional quantum Hall edges has a universal linear dependence on the current through the contact. In contrast, the temperature at eventual equilibrium scales as the square root of the power dissipating at the point contact. I propose to use this distinction to detect these intriguing nonequilibrium states.

Nonadiabatic charge pumping through a single-level quantum dot with periodically modulated parameters is studied theoretically. By means of a quantum-master-equation approach the full counting statistics of the system is obtained. We find a trinomial-probability distribution of the charge transfer, which adequately describes the reversal of the pumping current by sweeping the driving frequency. Further, we derive equations of motion for current and noise and solve those numerically for two different driving schemes. Both show interesting features, which can be fully analyzed due to the simple and generic model studied.

A complete structural solution of the bilayer iridate compound ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$ presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic moment in the basal plane. In this paper, we present single crystal neutron diffraction and rotational anisotropy second harmonic generation measurements unveiling a lower, monoclinic symmetry inherent to ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$. Combined with density functional theory, our measurements identify the correct structural space group as No. 15 (C2/c) and provide clarity regarding the local symmetry of ${\mathrm{Ir}}^{4+}$ cations within this spin-orbit Mott material.

Using the first-principles density functional approach, we investigate a material ${\mathrm{Pr}}_2{\mathrm{MgIrO}}_6$ (PMIO) of double-perovskite structure synthesized recently. According to the calculations, PMIO is a magnetic Mott-Hubbard insulator with ${\mu }_{\mathrm{tot}}\simeq 6{\mu }_{\mathrm{B}}$ per unit cell influenced by the cooperative effect of spin-orbit coupling (SOC) and Coulomb interactions of Ir-$5d$ and Pr-$4f$ electrons, as well as the crystal field. When Pr is replaced with Sr gradually, the system exhibits half-metallic (HM) states desirable for spintronics applications. In ${\left[{\mathrm{Pr}}_{2-x}{\mathrm{Sr}}_x{\mathrm{MgIrO}}_6\right]}_2$, HM antiferromagnetism (HMAFM) with zero magnetic moment in the unit cell is obtained for $x=1$, whereas for $x=0.5$ and 1.5 HM ferrimagnetism (HMFiM) is observed with ${\mu }_{\mathrm{tot}}\simeq 3{\mu }_{\mathrm{B}}$ and ${\mu }_{\mathrm{tot}}\simeq -3{\mu }_{\mathrm{B}}$ per unit cell respectively. It is emphasized that the large exchange splitting between spin-up and spin-down bands at the Fermi level makes the half-metallicity possible even with strong SOC.

By means of ab initio calculations, we investigated structural and magnetic properties of Pd and Rh thin films, determining their lattice parameters and epitaxial stresses when they are grown on various substrates, and provided a comparison with available experimental data. Further, we studied in detail the magnetic properties of Pd in the higher-energy hcp structure and of Rh in the higher-energy bcc structure. The results predict that the $\mathrm{hcp}\left(11\overline{2}0\right)$ Pd films [grown by epitaxy on the Nb(001) substrate] should not be ferromagnetically ordered. Concerning the hcp Pd, we mainly investigated the influence of the hcp $c/a$ ratio on the hcp film stability and on the ferromagnetic order. It turns out that the $c/a$ ratio has to be below 1.622 to induce the ferromagnetic order in hcp Pd. We proposed a technological route for obtaining ferromagnetic $\mathrm{hcp}\left(11\overline{2}0\right)$ Pd films and explained the experimentally observed ferromagnetism in twinned Pd nanoparticles induced by strain. We also found that bcc Rh is ferromagnetically ordered, but it cannot be stabilized in the form of thin films. Therefore, we investigated the dependence of ferromagnetic order in bct Rh on the tetragonal $c/a$ ratio and compared our results with experiments performed on Rh/Fe(001) multilayers.