Charge-to-spin conversion by topological surface states of amorphous Gd-alloyed Bi_xSe_1-x

Topological insulators with large spin-orbit coupling are promising material candidates for efficient charge-spin interconversion [1,2]. Recently, large spin-orbit torque has been observed in amorphous materials [3] and topological states are predicted and demonstrated in the amorphous system [4,5]. Here we report the charge-to-spin conversion (SCC) in the amorphous Gd-alloyed Bi_xSe_1-x (BSG)/CoFeB bilayer [6]. The maximum SCC efficiency is 0.035 nm for the inverse Edelstein length, measured by spin pumping. Clear evidence of SCC is also observed by the THz time-domain spectroscopy. By studying the dependence of SCC efficiency on BSG thickness, we find the SCC could originate from the topological surface states of BSG. In addition, the angle-resolved photoemission spectroscopy on BSG shows dispersive two-dimensional surface states, which further supports the existence of amorphous topological states in the BSG. Our studies provide a new path toward the search of amorphous topological materials for spintronic applications.



References

[1] M. Dc et al. Nature materials 17.9 (2018).

[2] NHD Khang et al. Nature materials 17.9 (2018).

[3] T. Peterson, et al. Physical Review Materials 5.4 (2021).

[4] A. Agarwala et al. Physical Review Letters 118.23 (2017).

[5] P. Corbae et al. Nature Materials 22.2 (2023).

[6] P. Sahu et al. ACS Applied Materials & Interfaces 15.32 (2023).