Current-induced exchange interactions and effective temperature in localized moment systems

We study theoretically the spin dynamics of a magnetic dimer serving as a contact between two electrodes. We find that the spin-spin coupling in the dimer can be dramatically modified from its equilibrium value. We show that the interaction can be tuned in such a way that it effectively changes its sign. The calculations show that, for large enough bias, the exchange interaction can even be changed from antiferromagnetic to ferromagnetic. The physical principles behind this result can be used as a new tool to achieve magneto-electric effects in molecular magnet systems.     

Multi-component fractional quantum Hall states in graphene: SU(4) versus SU(2)

Because of the spin and Dirac-valley degrees of freedom, graphene allows the observation of one-, two- or four-component fractional quantum Hall effects in different parameter regions. We address the stability of various states in the SU(2) and SU(4) limits. In the SU(4) limit, we predict that new low-energy Goldstone modes determine the stability of the fractional quantum Hall states at 2/5, 3/7, etc; SU(4) skyrmions are not found to be relevant for the low-energy physics. These results are discussed in light of experiments.     

Electronic structure and elasticity of Z-phases in the Cr-Nb-V-N system

Structural properties and energetics of Cr-based Z-phases (CrNbN, Cr(Nb,V)N and CrVN) were investigated using the Vienna ab?initio simulation package (VASP) code employing the projector augmented wave (PAW) pseudopotentials by means of both local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange and correlation term. The geometry of all studied phases including NbN, VN and elemental constituents (nonmagnetic bcc Nb and V and antiferromagnetic bcc Cr) was fully relaxed, providing the equilibrium structure parameters and total energies. The calculated lattice parameters of Z-phases correspond very well to the experimental data and decrease with increasing molar fraction of vanadium. Enthalpies of formation show that all three Z-phases are stable at T?=?0?K. The electronic structures of Z-phases including densities of states and charge densities were analysed. The calculated bulk moduli and elastic constants were used to evaluate stability conditions and elastic anisotropy ratios. It was confirmed that Z-phases are mechanically stable. Additional information on ductility was obtained from Cauchy pressures, Pugh ratios, Young moduli, and Poisson ratios. The ductility evaluated using the Pugh ratio decreases with number of vanadium atoms.     

First-principle calculations of the Berry curvature of Bloch states for charge and spin transport of electrons

Recent progress in wave packet dynamics based on the insight of Berry pertaining to adiabatic evolution of quantum systems has led to the need for a new property of a Bloch state, the Berry curvature, to be calculated from first principles. We report here on the response to this challenge by the ab initio community during the past decade. First we give a tutorial introduction of the conceptual developments we mentioned above. Then we describe four methodologies which have been developed for first-principle calculations of the Berry curvature. Finally, to illustrate the significance of the new developments, we report some results of calculations of interesting physical properties such as the anomalous and spin Hall conductivity as well as the anomalous Nernst conductivity and discuss the influence of the Berry curvature on the de Haas-van Alphen oscillation.     

Full potential x-ray absorption calculations using time dependent density functional theory

We report the implementation of a fully relativistic time dependent density functional theory (TDDFT) method for carrying out x-ray absorption spectroscopy calculations for extended systems. This is the first time that a TDDFT simulation of x-ray absorption in extended systems has featured a full potential ground state calculation. We prove that this unusual feature of the TDDFT implementation unequivocally yields improvement over the previous muffin-tin calculation methods.     

Heterogeneous crystallization in colloids and complex plasmas: the role of binary mobilities

Both charged colloidal suspensions and complex (dusty) plasmas represent classical many-body strongly coupled Coulomb systems. Here we discuss their basic properties and focus on their heterogeneous crystallization from an undercooled melt. In particular, a model with different mobilities is proposed which is realizable in binary mixtures of charged particles. Within this binary-mobility model, the crystallization behaviour near a structured wall is explored by Brownian dynamics computer simulations. As a result, the propagation velocity of the crystal-fluid interface is a nonmonotonic function of the mobility ratio (if expressed in terms of an averaged mobility).     

Extrinsic electronic transport in La0.7(Sr,Ca)0.3MnO3 films deposited on step edges and bicrystal substrates

In this paper, the electronic transport of La(0.7)(Sr,Ca)(0.3)MnO(3) films grown by pulsed laser deposition on a LaAlO(3)(001) substrate with deep parallel structured steps and a 30° symmetric bicrystal SrTiO(3)(001) substrate have been discussed. The electronic transport properties have been related to the well-known extrinsic transport of bulk manganite compounds. The spin-glass-like behavior with a characteristic peak at 20 K and domain formation at the grain boundary is observed. Further, it has been quantified from the resonant tunneling model that mixed magnetic interactions play a significant role in the manganite films deposited on step edges.     

Intrinsic contribution to spin Hall and spin Nernst effects in a bilayer graphene

We consider intrinsic contributions to the spin Hall and spin Nernst effects in a bilayer graphene. The relevant electronic spectrum is obtained from the tight binding Hamiltonian, which also includes the intrinsic spin-orbit interaction. The corresponding spin Hall and spin Nernst conductivities are compared with those obtained from effective low-energy k ?p and reduced Hamiltonians, which are appropriate for states in the vicinity of the Fermi level of a neutral bilayer graphene. Both conductivities are determined within the linear response theory and Green function formalism. The influence of an external voltage between the two atomic sheets is also considered. The results reveal a transition from the topological spin Hall insulator phase at low voltages to conventional insulator phase at larger voltages.     

Coexistence of ergodicity and nonergodicity in LaFeO(3)-modified Bi(1/2)(Na(0.78)K(0.22))(1/2)TiO(3) relaxors

The effect of LaFeO(3) addition to Bi(1/2)(Na(0.78)K(0.22))(1/2)TiO(3) ceramics on the phase stability and macroscopic functional properties was investigated. Similarly to other chemical modifiers known in the literature, LaFeO(3) addition suppresses an electric-field-induced long-range ferroelectric order, giving rise to a giant unipolar strain of ～0.3% at 2?mol% LaFeO(3) addition. Time-dependent changes in polarization and strain hysteresis loops both during successive electrical cycling and after removal of the electric field suggest that a specimen with 2?mol% LaFeO(3) consists of both ergodic and nonergodic phases, which is unique among the known relaxor materials.