Incipient localization of charge carriers in the two-dimensional electron system in LaAlO3/SrTiO3 under hydrostatic pressure

The two-dimensional electron system (2DES) in LaAlO3/SrTiO3 (LAO/STO) heterostructures, showing superconductivity below 200 mKat ambient pressure, displays incipient localization under hydrostatic pressure p. Even small p significantly affects the transport properties for 10 K < T < 100 K where impurity scattering dominates. The distinct T dependence of impurity scattering results in a minimum of the sheet resistance R-s(T), which has been often attributed to Kondo scattering. We show that the strong suppression of the dielectric permittivity epsilon(p) of STO enhances impurity scattering via the loss of screening and leads to incipient localization of charge carriers with increasing hydrostatic pressure. For T < 10 K negative logarithmic corrections to the conductance are attributed to electron-electron interaction. Weak localization and antilocalization, if present, are dominated by the pivotal role of impurity scattering by, e.g., oxygen vacancies, for the transport properties of the 2DES in LAO/STO heterostructures. This interpretation is favorited by exploiting the strong dependence of the dielectric permittivity of STO on pressure. Measurements of the magnetoresistance corroborate this interpretation.