Recovering Metallicity in A4C60: The Case of Monomeric Li4C60

TL;DR

This paper investigates the metallicity restoration in high-temperature Li4C60, revealing the importance of lattice symmetry and Jahn-Teller effects, and suggesting potential for new superconducting fullerides.

Contribution

It demonstrates that high-temperature Li4C60 exhibits metallic behavior due to charge transfer and lattice symmetry, challenging previous insulating assumptions for A4C60 compounds.

Findings

Li4C60 becomes metallic at T > 600 K

Lattice symmetry influences transport properties

Jahn-Teller effects impact band structure

Abstract

The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T > 600 K, show that its fcc structure is associated with a complete (4e) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination. Moreover, they suggest the present system as a potential precursor to a new class of superconducting fullerides.