Abstract
We report on a metal-insulator transition in the LaAlO${}_{3}$-SrTiO${}_{3}$ interface electron system, of which the carrier density is tuned by an electric gate field. Below a critical carrier density ${n}_{c}$ ranging from 0.5 to $1.5\ifmmode\times\else\texttimes\fi{}{10}^{13}/{\mathrm{cm}}^{2}$, LaAlO${}_{3}$-SrTiO${}_{3}$ interfaces, forming drain-source channels in field-effect devices, are nonohmic. The differential resistance at zero channel bias diverges within a 2$%$ variation of the carrier density. Above ${n}_{c}$, the conductivity of the ohmic channels has a metal-like temperature dependence, while below ${n}_{c}$ conductivity sets in only above a threshold electric field. For a given thickness of the LaAlO${}_{3}$ layer, the conductivity follows a ${\ensuremath{\sigma}}_{0}\ensuremath{\propto}(n\ensuremath{-}{n}_{c})/{n}_{c}$ characteristic. The metal-insulator transition is found to be distinct from that of the semiconductor 2D systems.
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