Topological Spintronics: Materials, Phenomena and Devices

The two-dimensional surface states of three-dimensional topological insulators such as Bi$_2$Se$_3$ and (Bi,Sb)$_2$Te$_3$ possess a spin texture that can potentially be exploited for spintronics applications. We provide a perspective on the emergence of ``topological spintronics,'' demonstrating how this spin texture can be engineered using either quantum tunneling between surfaces [1] or by breaking time-reversal symmetry [2]. We then discuss recent experiments that show striking spintronic phenomena useful for proof-of-concept devices, including a spin-orbit torque of record efficiency at room temperature [3] and an electrically-gated ``giant anisotropic magnetoresistance'' at low temperature [4].\\[4pt] This work was carried out in collaboration with A. Richardella, S.-Y. Xu, M. Neupane, A. Mellnik, A. Kandala, J. S. Lee, D. M. Zhang, M. Z. Hasan and D. C. Ralph. We acknowledge funding from the DARPA Meso program, ONR and C-SPIN (under sponsorship of MARCO and DARPA). \\[4pt] [1] M. Neupane, A. Richardella {\it et al.}, Nature Communications {\bf 5}, 3841 (2014).\\[0pt] [2] S.-Y. Xu {\it et al.}, Nature Physics {\bf 8}, 616 (2012).\\[0pt] [3] A. Mellnik, J. S. Lee, A. Richardella {\it et al.}, Nature {\bf 511}, 449 (2014).\\[0pt] [4] A. Kandala, A. Richardella, {\it et al.}, submitted.