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

The two-dimensional electron system (2DES) in $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ (LAO/STO) heterostructures, showing superconductivity below 200 mK at ambient pressure, displays incipient localization under hydrostatic pressure $p$. Even small $p$ significantly affects the transport properties for $10\phantom{\rule{0.16em}{0ex}}\mathrm{K}lTl100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ where impurity scattering dominates. The distinct $T$ dependence of impurity scattering results in a minimum of the sheet resistance ${R}_{\mathrm{s}}(T)$, which has been often attributed to Kondo scattering. We show that the strong suppression of the dielectric permittivity $\ensuremath{\varepsilon}(p)$ of STO enhances impurity scattering via the loss of screening and leads to incipient localization of charge carriers with increasing hydrostatic pressure. For $Tl10\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ 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.