Modulation of manganite thin-film properties by strontium titanate excitons*

A comprehensive investigation of the optical, electronic and magnetic properties of La_0.7Sr_0.3MnO₃ films on SrTiO₃ (LSMO/STO) and other substrates is conducted using multiple experimental techniques. There is a significant difference in the optical properties of LSMO/STO even in the case of 87.2nm-thick LSMO/STO as compared to those of LSMO on other substrates. We observed interesting excitonic features in the LSMO/STO thin-film at ~4eV. This could be due to formation of anomalous charged excitonic complexes. Based on spectral-weight transfer analysis, anomalous excitonic effects from STO strengthen the electronic-correlation in LSMO films. This results in optical spectral changes related to intrinsic Mott-Hubbard properties in the manganite films. While lattice strain influences the optical properties of the LSMO thin-films, strong e-e and e-h interactions from the substrate play a significant role as well.