Theoretical model for the structural phase transition at the metal- insulator transition in polymerized KC60

TL;DR

This paper presents a theoretical model explaining the structural phase transition in polymerized KC60 at 50 K, linking it to charge density waves and ion displacements that drive the metal-insulator transition.

Contribution

It introduces a specific superstructure model based on orientational charge density waves and ion displacements, unique to KC60's space group, explaining the metal-insulator transition.

Findings

Superstructure results from charge density waves and K+ displacements.

The mechanism is specific to KC60's space group Pmnn.

The model explains the metal-insulator transition in KC60.

Abstract

The recently discovered structural transition in polymerized KC60 at about 50 K results in a doubling of the unit cell volume and accompanies the metal-insulator transition. Here we show that the (a+c,b,a-c) superstructure results from small orientational charge density waves along the polymer chains and concomitant displacements of the surrounding K+ ions. The effect is specific for the space group Pmnn of KC60 and is absent in Rb- and CsC60 (space group I2/m). The mechanism is relevant for the metal-insulator transition.