Role of percolation in the conductance of electrolyte-gated SrTiO ₃

We study the electrolyte-gate-induced conductance at the surface of SrTiO 3(001). We find two distinct transport regimes as a function of gate voltage. At high carrier densities, a percolative metallic state is induced in which, at low temperatures, clear signatures of a Kondo effect are observed. At lower carrier densities, the resistance diverges at low temperatures and can be well described by a 2D variable range hopping model. We postulate that this derives from nonpercolative transport due to inhomogeneous electric fields from imperfectly ordered ions at the electrolyte-oxide interface. © 2012 American Physical Society.