Enhanced conductivity and metal-insulator transition of ultrathin CaRuO3 in superlattices

Transport characteristics of CaRuO3 (CRO)/SmFeO3 (SFO) superlattices are studied as a function of the thickness of CRO (0.8 nm <= t(CRO) <= 3.2 nm). An abrupt enhancement of the conductivity is observed on superlattices, although ultrathin CRO film show a very high resistance and SFO single layer is insulating. The superlattices with tCRO between 2.0 and 3.2 nm retain a metallic state. As tCRO decreases to 1.6 nm or even thinner in superlattices, the metallic state turns to insulating state. The metal-insulator transition could be attributed to the comparable scale for the disorder length and the electron travel distance at small t(CRO) value, which causes a change from weak localization to strong localization.