Optical probe of strong correlations in LaNiO${}_3$ thin films

Abstract

The optical properties of LaNiO${}_3$ thin films are investigated over a wide energy and temperature range. Thin films of varying thickness were epitaxially grown by pulsed laser deposition on LaAlO${}_3$ and SrTiO${}_3$ substrates. The optical conductivity data of the films reveal a number of interband transitions above 1 eV which are in good agreement with band structure calculations. No well defined Drude peak is observed however, in stark contrast with LDA theory predicting a finite density of states at the Fermi energy. This experimental finding of a vanishing Drude spectral weight, compared to a finite electron kinetic energy obtained from band structure calculations, highlights the importance of strong electronic correlations in LaNiO${}_3$.