Gate tunable spin-orbit coupling and weak antilocalization effect in an epitaxial La2/3Sr1/3MnO3 thin film

Epitaxial $\mathrm{L}{\mathrm{a}}_2/3\mathrm{S}{\mathrm{r}}_1/3\mathrm{Mn}{\mathrm{O}}₃$ (LSMO) films have been grown on $\mathrm{SrTi}{\mathrm{O}}₃$ (001) substrates via pulsed laser deposition. In a 22-nm-thick LSMO film with a low residual resistivity of ${\ensuremath{\rho}}₀\ensuremath{\approx}59\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$, we found a zero-field dip in the magnetoresistance (MR) below 10 K, manifesting the weak antilocalization (WAL) effect due to strong spin-orbit coupling (SOC). We have analyzed the MR data by including the D'yakonov-Perel' spin-relaxation mechanism in the WAL theory. We explain that the delocalized spin-down electron sub-band states play a crucial role for facilitating marked SOC in clean LSMO. Moreover, we find that the SOC strength and gate voltage tunability are similar to those in a two-dimensional electron gas at the $\mathrm{LaAl}{\mathrm{O}}₃/\mathrm{SrTi}{\mathrm{O}}₃$ interface, indicating the presence of an internal electric field near the LSMO/$\mathrm{SrTi}{\mathrm{O}}₃$ interface. In a control measurement on a 5-nm-thick high resistivity $({\ensuremath{\rho}}₀\ensuremath{\approx}280\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})$ LSMO film, we observe only a small zero-field peak in MR from weak localization effect, indicating negligible SOC.