Possible Enhancement of Superconductivity in Ambient-Pressure La$_3$Ni$_2$O$_7$ Thin Film

TL;DR

This study uses the FLEX approximation to analyze how Fermi-surface nesting influences superconductivity in La$_3$Ni$_2$O$_7$ thin films, suggesting nesting-driven spin fluctuations could enhance $s{ extpm}$-wave pairing.

Contribution

It provides a theoretical analysis of the pairing mechanism in La$_3$Ni$_2$O$_7$ thin films, highlighting the role of Fermi-surface nesting in enhancing superconductivity.

Findings

Emergence of a $ ext{ extdelta}$ pocket enhances nesting.

Nesting between pockets promotes $s{ extpm}$-wave pairing.

Nesting-driven spin fluctuations may boost superconductivity.

Abstract

As an unconventional superconducting system capable of reaching 60 K under ambient pressure, the La$_3$Ni$_2$O$_7$ thin film superconductor has recently become a focal point in the field of superconductivity, calling for further theoretical exploration of its possible pairing mechanisms. In this work, we employ the fluctuation exchange (FLEX) approximation to systematically analyze the superconducting properties of a previously proposed two-site, two-orbital model for the La$_3$Ni$2$O$7$ thin film in the weakly correlated regime, with particular emphasis on its dependence on hole doping. Through a more detailed examination of the Fermi-surface topology, we find that when a $\delta$ pocket composed of the $d_{z^{2}}$ antibonding orbital emerges near the $\Gamma$ point, its nesting with the $\gamma$ pocket, together with the nesting between the $\alpha$ and $\beta$ pockets, leads to a mutual enhancement of $s{\pm}$-wave pairing at the corresponding wave vector. Furthermore, we propose that this nesting-driven enhancement of spin-fluctuation-induced pairing may provide a viable mechanism for enhancing superconductivity.