Novel metal-insulator-transition at the SrTiO3/SmTiO3 interface

We report on a metal-insulator transition (MIT) that is observed in an electron system at the SmTiO3/SrTiO3 interface. This MIT is characterized by an abrupt transition at a critical temperature, below which the resistance changes by more than an order of magnitude. The temperature of the transition systematically depends on the carrier density, which is tuned from ~ 1x10^14 cm^-2 to 3x10^14 cm^-2 by changing the SmTiO3 thickness. Analysis of the transport properties shows non-Fermi liquid behavior and mass enhancement as the carrier density is lowered. We compare the MIT characteristics with those of known MITs in other materials systems and show that they are distinctly different in several aspects. We tentatively conclude that both long range Coulomb interactions and the fixed charge at the polar interface are likely to play a role in this MIT. The strong dependence on the carrier density makes this MIT of interest for field-tunable devices.