Evidence for mass renormalization in LaNiO$"" sub 3_: an in situ soft   x-ray photoemission study of epitaxial films
  We investigate the electronic structure of high-quality single-crystal LaNiO$_3$ (LNO) thin films using in situ photoemission spectroscopy (PES). The in situ high-resolution soft x-ray PES measurements on epitaxial thin films reveal the intrinsic electronic structure of LNO. We find a new sharp feature in the PES spectra crossing the Fermi level, which is derived from the correlated Ni 3$d$ $e_g$ electrons. This feature shows significant enhancement of spectral weight with decreasing temperature. From a detailed analysis of resistivity data, the enhancement of spectral weight is attributed to increasing electron correlations due to antiferromagnetic fluctuations. 
K. Horiba, R. Eguchi, M. Taguchi, A. Chainani, A. Kikkawa, Y. Senba,   H. Ohashi, S. Shin