Ferroelectricity in (K@C$_{60}$)$_n$

TL;DR

This paper presents a theoretical study predicting ferroelectricity in long-chain (K@C60)n due to electron-phonon interactions, with a phase diagram in the narrow bandwidth regime.

Contribution

It introduces a mean field theory analysis showing ferroelectric ground state stability caused by pseudo-Jahn-Teller effects in (K@C60)n.

Findings

Ferroelectric ground state is stable in the model.

Pseudo-Jahn-Teller mixing drives ferroelectricity.

Phase diagram for the narrow bandwidth regime is derived.

Abstract

A theoretical analysis of the ground state of long-chain (K@C$_{60}$)$_n$ is presented. Within mean field theory, a ferroelectric ground state is found to be stable because of the pseudo-Jahn-Teller mixing of the b$_{1u}$ and the b$_{2g}$ band with a zone-center optical phonon involving the displacement of the endohedral K^+ ions. A phase diagram for this model is derived in the narrow bandwidth regime.