Metal/SrTiO₃ two-dimensional electron gases for spin-to-charge conversion

An emerging direction in oxide research aims at probing interfaces with two-dimensional electron gases (2DEGs) possessing a finite Rashba spin-orbit coupling. This allows the interconversion of spin and charge through the direct and inverse Edelstein and spin Hall effects which play a key role for future spintronics devices. A very simple path to achieve SrTiO₃-based 2DEGs is by deposition of reactive metals on SrTiO₃. Here we compare the formation and properties of 2DEGs generated in SrTiO₃ by the growth of Al, Ta, and Y ultrathin films by magnetron sputtering. X-ray photoelectron spectroscopy study revealed the quantification of reduced Ti states associated with 2DEG formation. The carrier densities are extracted from magnetotransport measurements. Finally, spin-charge conversion has been measured and compared between different metal/SrTiO₃ systems by spin-pumping experiments where the samples were capped with an extra NiFe layer. The trends observed for different metal/SrTiO₃ systems provide a systematic study as a function of the carrier density and the transparency of the metal oxide tunnel barrier.