Spectral Weight Redistribution in (LaNiO{sub 3}){sub n}/(LaMnO{sub 3}){sub 2} Superlattices from Optical Spectroscopy.

Authors

Abstract

We have studied the optical properties of four (LaNiO3)(n)/(LaMnO3)(2) superlattices (SL) (n = 2, 3, 4, 5) on SrTiO3 substrates. We have measured the reflectivity at temperatures from 20 to 400 K, and extracted the optical conductivity through a fitting procedure based on a Kramers-Kronig consistent Lorentz-Drude model. With increasing LaNiO3 thickness, the SLs undergo an insulator-to-metal transition (IMT) that is accompanied by the transfer of spectral weight from high to low frequency. The presence of a broad midinfrared band, however, shows that the optical conductivity of the (LaNiO3)(n)/(LaMnO3)(2) SLs is not a linear combination of the LaMnO3 and LaNiO3 conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites.