Detecting the Surface Spin Polarization State of Topological Materials by Using Resonant X-ray Reflectometry

Abstract

The topological insulator as a promising and low cost next generation spintronic device attracts lots of attentions recently. The spin-momentum locking is a characteristic feature of topological materials at the surface states. One consequence of spin-momentum locking is that a current induces a non-equilibrium spin polarization on the surface of a topological insulator. In turn, this spin-polarization can be used to manipulate the magnetization of materials that are in proximity to the surface of a topological insulator. Notably, the spin-orbit torque caused by topological material has a relative low cost of current, compared with heavy metals. Resonant X-ray Reflectometry (RXR) is used to probe this phenomena in a multilayer thin film comprised of a 3D topological insulator slab in contact with a soft magnet. By measuring x-ray reflectivity at several element edges using circularly polarized light, the polarized spin states near the interface between topological insulator and magnet are able to be probed, hence the current induced spin polarization of topological insulator surface states could be potentially determined.