Opto-electronic detection of magnetization in topological insulator/magnetic insulator heterostructure devices

Topological Insulators (TIs) are of interest for ‘topological spintronics’ applications due to the inherent spin texture of the surface states, the large spin-orbit coupling, and the high spin current-to-charge current conversion efficiency. Heterostructure devices that interface TIs with magnetic insulators (MIs) are of particular interest because the charge current in the TI layer is not shunted by the MI layer. However, the latter characteristic also makes it challenging to electrically detect the magnetization state of hybrid TI/MI devices that use charge-spin conversion for manipulating the magnetization of the MI layer. To solve this problem, we demonstrate that the magnetic state of an insulating yttrium iron garnet thin film can be probed by using a spin-dependent photocurrent generated optically in a proximal TI ((Bi,Sb)₂Te₃). We study the magnetic field-dependence of the photocurrent as a function of light intensity, light wavelength, and chemical potential over a temperature range from 25 K to room temperature. We account for our observations using the recently discovered photo-spin-voltaic effect [Nat. Phys. 12, 861 (2016)].