Spectral weight redistribution in (LaNiO3)n/(LaMnO3)2 superlattices from optical spectroscopy

الأصل · EN

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 K 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 mid-infrared 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.