Electronic correlations and partial gap in the bilayer nickelate La₃Ni₂O₇.

Abstract

The discovery of superconductivity with a critical temperature of about 80 K in La₃Ni₂O₇ single crystals under pressure has received enormous attention. La₃Ni₂O₇ 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 La₃Ni₂O₇ 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- <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>d</mi></mrow> <mrow><mn>3</mn> <msup><mrow><mi>z</mi></mrow> <mrow><mn>2</mn></mrow> </msup> <mo>-</mo> <msup><mrow><mi>r</mi></mrow> <mrow><mn>2</mn></mrow> </msup> </mrow> </msub> </math> orbital is removed due to the transition at T ^∗. Our experimental results provide pivotal information for understanding the transition at T ^∗ and superconductivity in La₃Ni₂O₇.