Dynamical Jahn--Teller instability in metallic fullerides

TL;DR

This paper demonstrates that dynamical Jahn-Teller instability occurs in metallic fullerides like K$_3$C$_{60}$ when electron-electron interactions exceed a critical threshold, affecting their orbital structure and Mott transition behavior.

Contribution

The study extends the Gutzwiller approach to include Jahn-Teller effects in correlated metals, revealing the presence of dynamical Jahn-Teller instability in cubic fullerides.

Findings

Dynamical Jahn-Teller instability develops when U exceeds a critical value.

The critical U is lower than current estimates, indicating instability in all cubic fullerides.

Orbital degeneracy plays a significant role in the Mott-Hubbard transition.

Abstract

Dynamical Jahn-Teller effect has escaped so far direct observation in metallic systems. It is particularly believed to be quenched also in correlated conductors with orbitally degenerate sites such as cubic fullerides. Here the Gutzwiller approach is extended to treat electron correlation over metals with Jahn-Teller active sites and applied to the investigation of the ground state of K$_3$C$_{60}$. It is shown that dynamical Jahn-Teller instability fully develops in this material when the interelectron repulsion $U$ on C$_{60}$ sites exceeds some critical value. The latter is found to be lower than the current estimates of $U$, meaning that dynamical Jahn-Teller effect takes place in all cubic fullerides. This leads to strong splitting of LUMO orbitals on C$_{60}$ sites and calls for reconsideration of the role of orbital degeneracy in the Mott-Hubbard transition in fullerides.