Electronic correlations and partial gap in the bilayer nickelate LaNiO.

The discovery of superconductivity with a critical temperature of about 80 K in LaNiO single crystals under pressure has received enormous attention. LaNiO is not superconducting under ambient pressure but exhibits a transition at T  ≃ 115 K. Understanding the electronic correlations and charge dynamics is an important step towards the origin of superconductivity and other instabilities. Here, our optical study shows that LaNiO features strong electronic correlations which significantly reduce the electron's kinetic energy and place this system in the proximity of the Mott phase. The low-frequency optical conductivity reveals two Drude components arising from multiple bands at the Fermi level. The transition at T  removes the Drude component exhibiting non-Fermi liquid behavior, whereas the one with Fermi-liquid behavior is barely affected. These observations in combination with theoretical results suggest that the Fermi surface dominated by the Ni- orbital is removed due to the transition at T . Our experimental results provide pivotal information for understanding the transition at T  and superconductivity in LaNiO.