Theoretical Model for the Structural Phase Transition and the Metal–Insulator Transition in Polymerized KC60

Abstract The recently discovered structural phase transition in polymerized KC60 at about 50 K leads to a doubling of the unit cell volume and is accompanied by a metal–insulator transition. Here, we show that the superstructure results from orientational charge density waves along the polymer chains and correlated displacements of the K+ ions. The presented model can also account for the metal–insulator transition. The effect is specific for the space group Pmnn of KC60 and is absent in both Rb‐ and CsC60 (space group I2/m), in agreement with the present experimental knowledge of these compounds.