The spin-Seebeck effect refers to voltage signals induced in metals by thermally driven spin currents in adjacent magnetic systems. We present a theory of the spin-Seebeck signal in the case where the conductor that supports the voltage signal is the topologically protected two-dimensional surface-state system at the interface between a ferromagnetic insulator (FI) and a topological insulator (TI). Our theory uses a Dirac model for the TI surface-states and assumes Heisenberg exchange coupling between the TI quasiparticles and the FI magnetization. The spin-Seebeck voltage is induced by the TI surface states scattering off the nonequilibrium magnon population at the surface of the semi-infinite thermally driven FI. Our theory is readily generalized to spin-Seebeck voltages in any two-dimensional conductor that is exchange-coupled to the surface of a FI. Surface-state carrier-density-dependent signal strengths calculated using Bi2Te3 and yttrium iron garnet material parameters are consistent with recent experiments.
@article{arxiv.1612.04916,
title = {Theory of the Spin Seebeck Effect at a Topological-Insulator/Ferromagnetic-Insulator Interface},
author = {Nobuyuki Okuma and Massoud Ramezani Masir and Allan H. MacDonald},
journal= {arXiv preprint arXiv:1612.04916},
year = {2017}
}