Modified spin relaxation mechanism by tunable coupling between interfacial two-dimensional electron gases in correlated oxide heterostructures

Control of spin relaxation is an important prerequisite for the successful implementation of spintronic devices in a materials system. We realized two directly coupled two-dimensional (2D) electron gases (2DEG-2DEG) in a $\mathrm{LaAl}{\mathrm{O}}₃\text{\ensuremath{-}}\mathrm{SrTi}{\mathrm{O}}₃$ heterostructure system and observed a modification of the spin relaxation mechanism by varying the coupling strength. A strong enhancement of the carrier density for separation distances below a critical thickness of 6 unit cells was revealed. Electric-field-dependent analysis demonstrated tuning from positive to negative magnetoresistance for large separation distances of 10 unit cells indicating Rashba-type spin-orbit coupling, while for small separation distances of only 1 unit cell the magnetoresistance always remained positive. Analysis of the spin-orbit relaxation time and elastic scattering time revealed a modification of the spin relaxation mechanism between Elliott-Yafet and D'yakonov-Perel' for separation distances of 1 and 10 unit cells, respectively. The tunable spin relaxation fits very well with the presence (or absence) of structural inversion symmetry in our coupled 2DEGs system for different separation distances.