The quasi two-dimensional electron gas (q-2DEG) 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 (La$_{ 0.3}$Sr$_{ 0.7}$)(Al$_{ 0.65}$Ta$_{ 0.35}$)O$_{ 0.3}$/SrTiO$_{ 0.3}$ (LSAT/STO) interface. Before oxygen annealing, the as-grown interface exhibits a high electron density and electron occupancy of two subbands: higher-mobility electrons ($\mu_1\approx{ 10^4}$ cm$^2$V$^{ -1}$s$^{ -1}$ at 2 K) occupy the lower-energy $3d_{ xy}$ subband, while lower-mobility electrons ($\mu_1\approx{ 10^3}$ cm$^{ 2}$V$^{ -1}$s$^{ -1}$ at 2 K) propagate in the higher-energy $3d_{ xz/yz}$-dominated subband. After removing oxygen vacancies by annealing in oxygen, only a single type of 3dxy electrons remain at the annealed interface, showing tunable Shubnikov-de Haas (SdH) oscillations below 9 T at 2 K and an effective mass of $0.7m_e$. By contrast, no oscillation is observed at the as-grown interface even when electron mobility is increased to $50,000$ cm$^{ 2}$V$^{ -1}$s$^{ -1}$ by gating voltage. Our results reveal the important roles of both carrier mobility and subband occupancy in tuning the quantum transport at oxide interfaces.
Categories: cond-mat.str-el