Nature of the metal--insulator transition in oxide interfaces

One of the many unusual properties of several two-dimensional (2D) oxide interface systems (e.g., LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}})$ is the presence of a metal--insulator transition (MIT). This feature contradicts the famous prediction of Abrahams, et al. that all two-dimensional systems must be insulating. Since the MIT is a quantum phase transition (one that occurs at T$=$0K) the transport properties should be independent of the chemical and structural details of the system. Indeed, recent work has demonstrated that a generic phase diagram for the 2D MIT can be constructed for two very different systems: 1) highly disordered RuO$_{\mathrm{2}}$ nanoskins and 2) plasma-functionalized graphene. This phase diagram consists of three regions: metallic, weakly localized insulator with conductivity, conductivity\textasciitilde logT, and strongly localized insulator. We will present details of the transport properties of the disordered RuO$_{\mathrm{2}}$ nanoskins and plasma-functionalized graphene near their respective MITs. We will then present transport results for several gated oxide interface systems near their MITs and compare them with those for the RuO$_{\mathrm{2}}$ nanoskins and functionalized graphene.