Fermi-Level-Dependent Charge-to-Spin Conversion of the Two-Dimensional Electron Gas at the γ - Al2O3/KTaO3 Interface

Abstract

Charge-to-spin conversion is crucial for the application of emerging spintronic devices. A two-dimensional electron gas (2DEG) at a complex oxide interface usually possesses strong Rashba spin-orbit coupling, and spin-momentum locking offers a great possibility for efficient charge-to-spin conversion through the Rashba-Edelstein effect. Here, we report the fabrication of metallic 2DEGs in \ensuremath{\gamma}-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{KTaO}}_{3}$ spinel/perovskite heterostructures and investigate the charge-to-spin conversion for Py/\ensuremath{\gamma}-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{KTaO}}_{3}$ devices using the technique of spin-torque ferromagnetic resonance. The sizable spin splitting of the band structure results in a large current-induced spin-orbit torque efficiency with values up to around 3.6 at 5 K and about 1.1 at 300 K, which are more than an order of magnitude higher than those of heavy metals (0.07 for $\mathrm{Pt}$ at 300 K). Moreover, both theoretical and experimental results show that the charge-to-spin conversion is strongly dependent on the position of the Fermi level. These results demonstrate that optimizing the band filling of a ${\mathrm{KTaO}}_{3}$-based 2DEG is crucial for maximizing the conversion efficiency.