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21世紀COEセミナー「Unified theory of anomalous Hall transport phenomena:intrinsic versus extrinsic mechanisms」

日時 平成19年(2007年)12月12日(水) 13:30〜
場所 理学部宇宙地球科学科棟(F棟)5階 F524
講師 小野田 繁樹 氏((独)理化学研究所)
題目 Unified theory of anomalous Hall transport phenomena:intrinsic versus extrinsic mechanisms
概要 The anomalous Hall effect (AHE) in ferromagnets has been a fundamental and intriguing issue in condensed-matter physics. However, the controversy on the mechanism has continued to this date. In this talk, a unified theory of the AHE is presented for ferromagnetic metals with dilute impurities at the zero temperature [1], using the Keldysh technique in the gauge-covariant Wigner space [2]. In the superclean case, the AHE is mostly due to the extrinsic skew-scattering contribution. When the Fermi level is located around an avoided-crossing of band dispersions split by the spin-orbit interaction and/or the scalar spin chirality, the intrinsic AHE is resonantly enhanced by the topological non-perturbative nature to the order of in 2D and in 3D with the lattice constant . Then, an extrinsic-to-intrinsic crossover occurs when the relaxation rate γ becomes comparable to the spin-orbit interaction energy. Further increasing γ, a scaling relation appears in the dirty regime. The present work reveals the two crossovers, which explains wide experimental results [3] beyond the conventional perturbation theory in the spin-orbit coupling [4]. The anomalous Nernst and thermal Hall effects are also studied [5]. The thermal Hall conductivity follows the electric Hall conductivity and the same crossovers occur. However, the thermoelectric Hall conductivity suffers from an appreciable skew-scattering contribution, which masks the Berry curvature of the Bloch wavefunction near the Fermi surface even in the intrinsic regime.
[1] S. Onoda, N. Sugimoto, and N. Nagaosa, Phys. Rev. Lett. 97, 126602 (2006).
[2] S. Onoda, N. Sugimoto, and N. Nagaosa, Prog. Theor. Phys. 116, 61 (2006).
[3] T. Miyasato et al., Phys. Rev. Lett. 99, 086602 (2007).
[4] J.M. Luttinger, Phys. Rev. 112, 739 (1958).
[5] S. Onoda et al., unpublished.

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