Superconductivity Emerging from Excitonic Mott insulator - Theory of Alkaline Doped Fullerene

TL;DR

This paper presents a theoretical study of superconductivity in alkaline doped fullerene, showing how excitonic Mott insulators can give rise to superconductivity through exciton melting, supported by variational Monte Carlo simulations.

Contribution

It introduces a three-orbital model derived from ab initio calculations and demonstrates the emergence of superconductivity from an excitonic Mott insulator state.

Findings

Reproduces experimental s-wave superconductivity in the model.

Shows transition to an excitonic Mott insulator with orbital symmetry breaking.

Identifies exciton melting as the mechanism behind superconductivity.

Abstract

A three-orbital model derived from the two-dimensional projection of the $ab$ $initio$ Hamiltonian for alkaline doped fullerene A$_3$C$_{60}$ with A=Cs,Rb,K is studied by a variational Monte Carlo method. We correctly reproduce the experimental isotropic s-wave superconductivity around the $ab$ $initio$ parameters. With narrowing the bandwidth, the transition to an insulator is also reproduced, where orbital symmetry is found to be spontaneously broken with emergence of an excitonic Mott insulator for two orbitals and an antiferromagnetic insulator nearly degenerate with a spin liquid for the third orbital. The superconductivity is a consequence of exciton melting.