Electronic correlations and superconducting instability in La$_3$Ni$_2$O$_7$ under high pressure

TL;DR

This study uses first-principles many-body theory to explore electronic properties of La$_3$Ni$_2$O$_7$ under high pressure, revealing a non-Fermi liquid state and strong spin fluctuations that suggest a superconducting instability.

Contribution

It provides a detailed theoretical analysis of the electronic correlations and potential superconducting mechanisms in La$_3$Ni$_2$O$_7$ under high pressure, highlighting the role of Ni-$d_{z^2}$ orbital correlations.

Findings

Discovery of a multi-orbital non-Fermi liquid state below 100 K.

Identification of strong spin fluctuations leading to superconducting tendencies.

Enhanced Ni-$d_{z^2}$ correlations explain increased $T_c$ under pressure.

Abstract

Motivated by the report of superconductivity in bilayer La$_3$Ni$_2$O$_7$ at high pressure, we examine the interacting electrons in this system. First-principles many-body theory is utilized to study the normal-state electronic properties. Below 100\,K, a multi-orbital non-Fermi liquid state resulting from loss of Ni-ligand coherence within a flat-band dominated low-energy landscape is uncovered. The incoherent low-temperature Fermi surface displays strong mixing between Ni-$d_{z^2}$ and Ni-$d_{x^2-y^2}$ orbital character. In a model-Hamiltonian picture, spin fluctuations originating mostly from the Ni-$d_{z^2}$ orbital give rise to strong tendencies towards a superconducting instability with $B_{1g}$ or $B_{2g}$ order parameter. The dramatic enhancement of $T_{\rm c}$ in pressurized La$_3$Ni$_2$O$_7$ is due to stronger Ni-$d_{z^2}$ correlations compared to those in the infinite-layer nickelates.