Spin to Charge Conversion at the Conducting TiO2 Surface.

The insulating TiO2 (100) surface was transformed into conducting state after Ar+ ion irradiation, which is due to the formation of oxygen vacancies. The thickness of the conducting layer is about 5 nm according to the transmission electron microscopy, and its surface with a spatial asymmetry hosts Rashba spin-orbit coupling. A permalloy (Py) thin film was then deposited onto the irradiated TiO2 by magnetron sputtering. In this Py/TiO2 sample, an inverse Rashba-Edelstein effect (IREE) induced voltage was detected, which converted the spin current injected from Py by spin pumping into the charge current (voltage) due to the spin-orbit coupling. Through the two-step measurement with sample flipping, the voltages of the IREE at different microwave frequency and power are separated from the spin rectification effect in the Py films. The inverse Rashba-Edelstein length λIREE, which is used to characterize the spin-to-charge current conversion efficiency, is calculated to be about 0.58 nm in this work. From the similarity of the parameter, we may conclude that the effect is universal in these two dimensional electron gas hosted by the surfaces or interfaces. [ABSTRACT FROM AUTHOR]