Interlayer Pairing in Bilayer Nickelates

TL;DR

This paper uses advanced quantum Monte Carlo simulations to demonstrate that interlayer pairing in a bilayer nickelate model leads to high-temperature superconductivity, supporting a simple effective model for La$_3$Ni$_2$O$_7$.

Contribution

It provides non-perturbative evidence that a bilayer two-orbital Hubbard-Hund model captures the superconducting behavior of La$_3$Ni$_2$O$_7$ with a dominant interlayer $s^$ pairing mechanism.

Findings

Identifies a leading $s^$ superconducting instability.

Shows interlayer pairing driven by interlayer spin fluctuations.

Validates a single-orbital bilayer Hubbard model as an effective low-energy description.

Abstract

The discovery of $T_c\sim 80$~K superconductivity in pressurized La$_3$Ni$_2$O$_7$ has launched a new platform to study high-temperature superconductivity. Using non-perturbative dynamic cluster approximation quantum Monte Carlo calculations, we characterize the magnetic and superconducting pairing behavior of a realistic bilayer two-orbital Hubbard-Hund model of this system that describes the relevant Ni $e_g$ states with physically relevant interaction strengths. We find a leading $s^\pm$ superconducting instability in this model and show that this state primarily arises from interlayer pairing in the $d_{3z^2-r^2}$ orbital that is driven by strong interlayer spin-fluctuations in that orbital. These results provide non-perturbative evidence supporting the picture that a simple single-orbital bilayer Hubbard model for the Ni $d_{3z^2-r^2}$ orbital provides an excellent low-energy effective description of the superconducting behavior of La$_3$Ni$_2$O$_7$.