Spin charge interconversion at surfaces of the topological insulator Bi-Sb-Te and the weyl antiferromagnet Mn₃Sn

Spin Hall effects are commonly utilized to interconvert between charge and spin currents. As an alternative mechanism for this interconversion, the spin-momentum locking at the Bi (111)/Ag interface [1] or the at the Dirac surface state of a topological insulator (TI) have recently been used for highly efficient interconversion [2].
Our recent study on the spin-torque ferromagnetic resonance in TI ((Bi_1-xSb_x)₂Te₃)/non-magnetic metal/ferromagnetic-metal tri-layer films in bulk insulating conditions revealed that the interface conversion coefficient q_ICS (nm^-1) from charge to spin currents stayed at a nearly constant large value of about 0.5 nm^-1 [2] except for the Dirac point, which is equivalent to the bulk spin Hall angle of about 50% for the quintuple layer thickness of 1 nm.
We also show recently found novel spin Hall effects in a Weyl antiferromagnet Mn₃Sn [4]. Th effects exhibit an anomalous sign change in the resulting spin accumulation when its triangularly ordered moments switch orientation. Our observations demonstrate that a novel type of contribution to the SHE (magnetic SHE, MSHE) and the inverse SHE (MISHE) that is absent in nonmagnetic materials can be dominant in some magnetic materials, including antiferromagnets.
First part of presentation is based on the collaboration with R. Yoshimi, A. Tsukazaki, Y. Fukuma, J. Matsuno, K. S. Takahashi, M. Kawasaki, and Y. Tokura. Second part is with T. Tomita, T. Higo, I. Muhammad, S. Nakatsuji, M. Kimata, K. Kondo, H. Chen, A. MacDonald.

[1] J.C. Rojas Sánchez et al, Nature Commun. 4, 2944 (2013).
[2] Lie, C. H. et al. Nature Nanotech. 9, 218 (2014).
[3] K. Kondou et al. Nature Physics12, 1027 (2016).
[4] K. Kuroda, T. Tomita, et al., Nature Materials 16, 1090 (2017).