Electrical properties and subband occupancy at the (La,Sr)(Al,Ta)O3/SrTiO3 interface

Abstract

The quasi-two-dimensional electron gas at oxide interfaces provides a platform for investigating quantum phenomena in strongly correlated electronic systems. Here, we study the transport properties at the high-mobility $(\mathrm{L}{\mathrm{a}}_{0.3}\mathrm{S}{\mathrm{r}}_{0.7})(\mathrm{A}{\mathrm{l}}_{0.65}\mathrm{T}{\mathrm{a}}_{0.35}){\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ interface. Before oxygen annealing, the as-grown interface exhibits a high electron density and electron occupancy of two subbands: higher-mobility electrons (${\ensuremath{\mu}}_{1}\ensuremath{\approx}{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at 2 K) occupy the lower-energy $3{d}_{\mathrm{xy}}$ subband, while lower-mobility electrons (${\ensuremath{\mu}}_{1}\ensuremath{\approx}{10}^{3}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at 2 K) propagate in the higher-energy $3{d}_{\mathrm{xz}/\mathrm{yz}}$-dominated subband. After removing oxygen vacancies by annealing in oxygen, only a single type of $3{d}_{\mathrm{xy}}$ electrons remain at the annealed interface, showing tunable Shubnikov--de Haas oscillations below 9 T at 2 K and an effective mass of $0.7{m}_{\mathrm{e}}$. By contrast, no oscillation is observed at the as-grown interface even when electron mobility is increased to $50\phantom{\rule{4pt}{0ex}}000\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ by gating voltage. Our results reveal the important roles of both carrier mobility and subband occupancy in tuning the quantum transport at oxide interfaces.