  Diluted oxide interface of LaAl1-xMnxO/SrTiO3 (LAMO/STO) provides a new way
of tuning the ground states of the interface between the two band insulators of
LAO and STO from metallic/superconducting to highly insulating. Increasing the
Mn doping level (x) leads to a delicate control of the carrier density as well
as a raise in the electron mobility and spin polarization. Herein, we
demonstrate a tunable Rashba spin-orbit coupling (SOC) and spin polarization of
LAMO/STO (0.2 <= x <= 0.3) by applying a back gate. The presence of SOC causes
the splitting of energy band into two branches by a spin splitting energy. The
maximum spin splitting energy depends on the Mn doping and decreases with the
increasing Mn content and then vanishes at x = 0.3. The carrier density
dependence of the spin splitting energy for different compositions shows a
dome-shaped behavior with a maximum at different normalized carrier density.
These findings have not yet been observed in LAO/STO interfaces. A fully
back-gate-tunable spin-polarized 2DEL is observed at the interface with x = 0.3
where only dxy orbits are populated (5.3E12 cm-2 <= ns <= 1.0E13 cm-2). The
present results shed light on unexplored territory in SOC at STO-base oxide
heterostructures and make LAMO/STO an intriguing platform for spin-related
phenomena in 3d-electron systems.
