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

Abstract

We have studied the optical properties of four (LaNiO${}_3$)${}_n$/(LaMnO${}_3$)${}_2$ superlattices (SL) ($n$=2, 3, 4, 5) on SrTiO${}_3$ 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 LaNiO${}_3$ 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 (LaNiO${}_3$)${}_n$/(LaMnO${}_3$)${}_2$ SLs is not a linear combination of the LaMnO${}_3$ and LaNiO${}_3$ conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites.

arXiv commentAccepted for publication in Phys. Rev. Lett. 5 pages, 5 figures

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• Charge transfer driven emergent phenomena in oxide heterostructures
• Charge density functional plus $U$ theory of LaMnO${}_3$: Phase diagram, electronic structure, and magnetic interaction
• Spin-orbital order in undoped manganite LaMnO3 at finite temperature
• Electrodynamic properties of an artificial heterostructured superconducting cuprate