arXiv subjects

Junji Fujimoto

Publications and source records attributed to Junji Fujimoto.

21 records · Page 2Linked to original sources

arXiv2017

Transport Coefficients of Dirac Ferromagnet: Effects of Vertex Corrections

As a strongly spin-orbit coupled metallic model with ferromagnetism, we have considered an extended Stoner model to the relativistic regime, named Dirac ferromagnet in three dimensions. In the previous paper~[Phys. Rev. B 90, 214418 (2014)], we studied the transport properties giving rise to the anisotropic magnetoresistance~(AMR) and the anomalous Hall effect~(AHE) with the impurity potential being taken into account only as the self-energy. The effects of the vertex corrections~(VCs) to AMR and AHE are reported in this paper. AMR is found not to change quantitatively when the VCs is considered, although the transport lifetime is different from the one-electron lifetime and the charge current includes additional contributions from the correlation with spin currents. The side-jump and the skew-scattering contributions to AHE are also calculated. The skew-scattering contribution is dominant in the clean case as can be seen in the spin Hall effect in the non-magnetic Dirac electron system.

cond-mat.mes-hall↗

arXiv2017

Intrinsic and Extrinsic Spin Hall Effects of Dirac Electrons

We investigate the spin Hall effect (SHE) of electrons described by the Dirac equation, which is used as an effective model near the $L$-points in bismuth. By considering short-range nonmagnetic impurities, we calculate the extrinsic as well as intrinsic contributions on an equal footing. The vertex corrections are taken into account within the ladder type and the so-called skew-scattering type. The intrinsic SHE which we obtain is consistent with that of Fuseya et al. [J. Phys. Soc. Jpn. 81, 93704 (2012)]. It is found that the extrinsic contribution dominates the intrinsic one when the system is (semi)metallic. The extrinsic SHE due to the skew scattering is proportional to $Δ/ n_{\rm i} u$, where $2Δ$ is the band gap, $n_{\rm i}$ is the impurity concentration, and $u$ is the strength of the impurity potential.

cond-mat.mes-hall↗

arXiv2014

Transport Properties of Dirac Ferromagnet

We propose a model ferromagnet based on the Dirac Hamiltonian in three spatial dimensions, and study its transport properties which include anisotropic magnetoresistance (AMR) and anomalous Hall (AH) effect. This relativistic extension allows two kinds of ferromagnetic order parameters, denoted by $\bm{M}$ and $\bm{S}$, which are distinguished by the relative sign between the positive- and negative-energy states (at zero momentum) and become degenerate in the non-relativistic limit. Because of the relativistic coupling between the spin and the orbital motion, both $\bm{M}$ and $\bm{S}$ induce anisotropic deformations of the energy dispersion (and the Fermi surfaces) but in mutually opposite ways. The AMR is determined primarily by the anisotropy of the Fermi surface (group velocity), and secondarily by the anisotropy of the damping; the latter becomes important for ${\bm M}=\pm{\bm S}$, where the Fermi surfaces are isotropic. Even when the chemical potential lies in the gap, the AH conductivity is found to take a finite non-quantized value, $σ_{ij} = -(α/3π^2 \hbar) ε_{ijk} S_k $, where $α$ is the (effective) fine structure constant. This offers an example of Hall insulator in three spatial dimensions.

cond-mat.mtrl-sci↗