Quantum transport theory of anomalous electric, thermoelectric, and thermal Hall effects in ferromagnets

Abstract

The mechanism of the anomalous Hall transport phenomena, if it is of the intrinsic or extrinsic origin, has been controversial. We present a unified theory of them for ferromagnetic metals with dilute impurities at the zero temperature, in terms of a quantum transport theory with the self-consistent T-matrix approximation. With the Fermi energy E_F and the spin-orbit interaction energy E_{SO} being fixed (E_F > E_{SO}), three regimes are found as a function of the scattering rate \hbar/\tau. (i) In the superclean case \hbar/\tau < u_{imp} E_{SO}D, the skew scattering from the vertex correction dominates the anomalous Hall conductivity \sigma_{xy}, where u_{imp} is the impurity potential strength and D is the density of states. With increasing \hbar/\tau, this extrinsic skew-scattering contribution rapidly decays. (ii) In the moderately dirty regime u_{imp}E_{SO}D < \hbar/\tau < E_{SO}, \sigma_{xy} is dominated by the intrinsic dissipationless Berry-phase contribution, which is resonantly enhanced to the order of e^2/\hbar when an accidental degeneracy of band dispersions around the Fermi level is lifted by the spin-orbit interaction. (iii) Further increasing \hbar/\tau, a \sigma_{xy}\propto\sigma_{xx}^{1.6} scaling appears, which has been verified by recent experiments. The themal and thermoelectric Hall conductivities are also discussed.