Spectral Weight Redistribution in (LaNiO3)n/(LaMnO3)2 Superlattices from Optical Spectroscopy.
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 LaMnO_{3} 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.
INSTM Udr Trieste-ST and Elettra-Sincrotrone Trieste S.C.p.A., Area Science Park, I-34012 Trieste, Italy.
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P
Di Pietro
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
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J
Hoffman
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
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A
Bhattacharya
CNR-IOM and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2, I-00185 Roma, Italy.
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S
Lupi
INSTM Udr Trieste-ST and Elettra-Sincrotrone Trieste S.C.p.A., Area Science Park, I-34012 Trieste, Italy.
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Perucchi