Do the A4c60 Fullerides Have a Broken-Symmetry Ground State?

TL;DR

This paper explores the insulating behavior of K4C60 fullerides, proposing a spin- or charge-density-wave state as an alternative to electron correlation explanations, challenging traditional band theory predictions.

Contribution

It introduces a theoretical scenario involving density-wave states to explain the insulating phase of K4C60, diverging from the common correlation-based explanations.

Findings

K4C60 exhibits insulating behavior contrary to band theory predictions.

A spin- or charge-density-wave state can account for the insulating phase.

The proposed model offers an alternative to electron correlation explanations.

Abstract

Band theory predicts both K3C60 and K4C60 to be metals; various experimental probes show that while K3C60 is indeed metallic, K4C60 appears to be insulating. The standard view of this apparent failure of the single-particle picture is that electron correlation is predominant. We describe an alternative scenario, motivated on theoretical grounds, which invokes a spin- or charge-density-wave state to explain the observed insulating behavior.