Optical detection of current-generated spin in topological insulators by magneto optical Kerr effect

The Dirac surface states of topological insulators (TIs) exhibit spin-momentum locking, where spin is locked at right angles to momentum, and hence an unpolarized charge current creates a net spin polarization. This polarization has been measured electrically using FM contacts [1]. Here we optically detect the current generated spin using magneto optic Kerr effect (MOKE). A thin layer of Al is deposited onto the TI films to enable the measurement of predominantly spins on the top surface, as Al is a good spin diffusion layer and optically opaque. Modulating the direction of the charge current through the TI and hence the direction of the spin, we observe corresponding response in the MOKE signal. This response is linear with current, exhibits a maximum at an intermediate Al thickness of ~20 nm, and exhibits a temperature dependence similar to that of electrical measurements. Furthermore, MOKE detection of magnetization switching of an adjacent ferromagnet from the current-generated spin in TI surface states via spin orbit torque will also be discussed at the meeting.
[1] C. H. Li et al., Nature Nanotech. 9, 218 (2014); Sci. Rep. 6, 29533 (2016); Nature Commun. 7, 13518 (2016).