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 t CRO between 2.0 and 3.2 nm retain a metallic state. As t CRO 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.