Unconventional Pairing from Local Orbital Fluctuations in Strongly Correlated A$_3$C$_{60}$

TL;DR

This paper investigates the pairing mechanism in A$_3$C$_{60}$, showing that local orbital fluctuations act as the pairing glue in these strongly correlated superconductors, aligning with experimental observations and the spin/orbital freezing theory.

Contribution

It demonstrates that local orbital fluctuations are the key pairing mechanism in A$_3$C$_{60}$, providing new insight into unconventional superconductivity in fullerides.

Findings

Local orbital fluctuations are enhanced in the superconducting state.

The fluctuation energy scale matches the low-energy spectral peak.

Results support the spin/orbital freezing theory of unconventional superconductivity.

Abstract

The pairing mechanism in A$_3$C$_{60}$ is investigated by studying the properties of a three-orbital Hubbard model with antiferromagnetic Hund coupling in the normal and superconducting phase. Local orbital fluctuations are shown to be substantially enhanced in the superconducting state, with a fluctuation energy scale that matches the low-energy peak in the spectral weight of the order parameter. Our results demonstrate that local orbital fluctuations provide the pairing glue in strongly correlated fulleride superconductors and support the spin/orbital freezing theory of unconventional superconductivity. They are also consistent with the experimentally observed universal relation between the gap energy and local susceptibility in a broad range of unconventional superconductors.