Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling

TL;DR

This paper investigates how lattice structure, Jahn-Teller effect, and Hund's rule coupling influence metal-insulator transitions in alkali-doped C60 compounds, revealing their complex interplay and effects on electronic phases.

Contribution

It provides a detailed analysis of how lattice structure and electron-phonon interactions affect the metal-insulator transition in A3C60 and A4C60, highlighting the partial cancellation between Jahn-Teller and Hund's effects.

Findings

Lattice structure determines metallic or insulating behavior.

Jahn-Teller coupling favors nonmagnetic insulating states.

Hund's rule coupling partially cancels Jahn-Teller effects.

Abstract

We study the influence of the lattice structure, the Jahn-Teller effect and the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb). The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60 (bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases) the value Uc of the Coulomb integral at which the metal-insulator transition occurs. There is an important partial cancellation between the Jahn-Teller effect and the Hund's rule coupling.