Optical Properties of (SrMnO3)n/(LaMnO3)2n Superlattices: An Insulator-to-Metal Transition Observed in the Absence of Disorder

We measure the optical conductivity sigma(1)(omega) of (SrMnO3)(n)/(LaMnO3)(2n) superlattices (SL) for n = 1 3 5 and 8 and 10 < T < 400 K Data show a T dependent Insulator to metal transition (IMT) for n <= 3 driven by the softening of a polaronic mid infrared band At n = 5 that softening is incomplete while at the largest period n = 8 compound the MIR band is independent of T and the SL remains insulating One can thus first observe the IMT in a Manganite system in the absence of the disorder due to chemical doping Unsuccessful reconstruction of the SL optical properties from those of the original bulk materials suggests that (SrMnO3)(n)/(LaMnO3)(2n) heterostructures give rise to a novel electronic state