We report the observation of ferromagnetic resonance-driven spin pumping signals at room temperature in three-dimensional topological insulator thin films -- Bi2Se3 and (Bi,Sb)2Te3 -- deposited by molecular beam epitaxy on yttrium iron garnet thin films. By systematically varying the Bi2Se3 film thickness, we show that the spin-charge conversion efficiency, characterized by the inverse Rashba-Edelstein effect length (lambda_IREE), increases dramatically as the film thickness is increased from 2 quintuple layers, saturating above 6 quintuple layers. This suggests a dominant role of surface states in spin and charge interconversion in topological insulator/ferromagnet heterostructures. Our conclusion is further corroborated by studying a series of YIG/(BiSb)2Te3 heterostructures. Finally, we use the ferromagnetic resonance linewidth broadening and the inverse Rashba-Edelstein signals to determine the effective interfacial spin mixing conductance and lambda_IREE.
@article{arxiv.1607.03872,
title = {Surface state dominated spin-charge current conversion in topological insulator/ferromagnetic insulator heterostructures},
author = {Hailong Wang and James Kally and Joon Sue Lee and Tao Liu and Houchen Chang and Danielle Reifsnyder Hickey and Andre Mkhoyan and Mingzhong Wu and Anthony Richardella and Nitin Samarth},
journal= {arXiv preprint arXiv:1607.03872},
year = {2016}
}