Spin-charge conversion induced by spin pumping into topological materials

Topological materials are promising candidates for novel spintronics devices which enable highly efficient spin-charge conversion, because spin direction and charge-flow direction are frequently coupled in topological materials owing to the strong spin-orbit interaction. In this presentation, we will give a talk on spin-charge conversion effects induced by spin pumping into two topological systems: (i) surfaces of topological insulators (Bi,Sb)₂(Te,Se)₃ and Sn-Bi₂Te₂Se [1,2]; and (ii) a Tl-Pb monolayer material [3].
Topological insulators (TIs) are novel materials whose interior is insulating, but the surface is conductive. On the surface state, spin direction and charge-flow direction have one-to-one correspondence, which should be suitable for the efficient spin-charge conversion. In our recent paper [1], we successfully demonstrated spin-charge conversion via spin pumping in ferromagnetic-metal/TI structure. Furthermore, in the subsequent paper [2], we clarified that the spin-charge conversion efficiency is greater for TI samples with higher bulk resistivity and longer surface mean free path. These works provide strong evidence that the observed spin-charge conversion takes place on the topological surface state.
Tl-Pb systems are interesting atomic-layer materials, which have good conductivity and also a strong Rashba spin-orbit coupling [4]. We recently demonstrated spin-charge conversion on Tl-Pb monolayer samples using spin pumping technique at room temperature [3]. Though the Tl-Pb monolayer is atomically thin, the efficiency is found to be comparable to TI systems. This result shows that the efficient spin-charge conversion is really possible for 2D Rashba systems.
[1] Y. Shiomi, et al. Phys. Rev. Lett. 113, 196601 (2014).
[2] K.T.Yamamoto, Y.Shiomi, et al. Phys. Rev. B 94, 024404 (2016).
[3] K.T. Yamamoto, Y.Shiomi, et al. in preparation (2017)
[4] A.V. Matetskiy, et al. Phys. Rev. Lett. 115, 147003 (2015).