Electronic correlations and partial gap in the bilayer nickelate La$_{3}$Ni$_{2}$O$_{7}$

TL;DR

This study investigates the electronic correlations and charge dynamics in La$_{3}$Ni$_{2}$O$_{7}$, revealing strong correlations, multiple Fermi surface components, and a transition affecting non-Fermi liquid behavior, which are crucial for understanding its superconductivity.

Contribution

The paper provides experimental evidence of strong electronic correlations and Fermi surface changes in La$_{3}$Ni$_{2}$O$_{7}$, advancing understanding of its transition and potential superconductivity.

Findings

Strong electronic correlations reduce electron kinetic energy.

Transition at T* removes a Drude component and alters non-Fermi liquid behavior.

Fermi surface dominated by Ni-$d_{3z^{2}-r^{2}}$ orbital is affected at T*.

Abstract

The discovery of superconductivity with a critical temperature of about 80~K in La$_{3}$Ni$_{2}$O$_{7}$ single crystals under pressure has received enormous attention. La$_{3}$Ni$_{2}$O$_{7}$ is not superconducting under ambient pressure but exhibits a transition at $T^{\ast} \simeq 115$~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 La$_{3}$Ni$_{2}$O$_{7}$ 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 $T^{\ast}$ 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-$d_{3z^{2}-r^{2}}$ orbital is removed due to the transition at $T^{\ast}$. Our experimental results provide pivotal information for understanding the transition at $T^{\ast}$ and superconductivity in La$_{3}$Ni$_{2}$O$_{7}$.