




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 
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 condensedmatter 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 gaugecovariant Wigner space [2]. In the superclean case, the AHE is mostly due to the extrinsic skewscattering contribution. When the Fermi level is located around an avoidedcrossing of band dispersions split by the spinorbit interaction and/or the scalar spin chirality, the intrinsic AHE is resonantly enhanced by the topological nonperturbative nature to the order of in 2D and in 3D with the lattice constant . Then, an extrinsictointrinsic crossover occurs when the relaxation rate γ becomes comparable to the spinorbit 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 spinorbit 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 skewscattering 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[5] S. Onoda et al., unpublished. 





