Giant spin-charge conversion in an all-epitaxial single-crystal-oxide Rashba LaTiO_3+δ/SrTiO₃ heterostructure

The two-dimensional electron gas formed at interfaces between SrTiO₃ (STO) and other insulating oxide materials has attracted much attention for large spin-charge conversion due to the sizable Rashba spin-orbit interaction. However, those insulating layers grown on STO prevent the propagation of the spin current injected from an adjacent ferromagnetic layer. Here, instead of the insulating layers, we use a strongly correlated polar-metal LaTiO_3+δ (LTO), demonstrating a giant conversion efficiency λ_IEE up to ~190 nm, which is the highest value among those reported for all materials [1].

For spin-pumping experiments, we have grown an all-epitaxial (La,Sr)MnO₃ (30 u.c.)/LTO (3 u.c.) heterostructure on an STO (001) substrate. Our spin-pumping measurements show λ_IEE up to 193.5 nm at 15 K. Our tight-binding calculation, in which the band parameters are optimized to reproduce the band structure observed by angle-resolved photoemission spectroscopy, can quantitatively explain the temperature dependence of λ_IEE. This highly efficient conversion highlights the new hidden inherent possibilities of oxide interfaces.

This work was supported by Grants-in-Aid for Scientific Research, CREST and PRESTO of JST, Spin-RNJ, and ANRI fellowship.

[1] S. Kaneta-Takada et al., Nat. Commun. 13, 5631 (2022).