Lattice distortion and energy level structures in doped C_{60} and C_{70} studied with the extended Su-Schrieffer-Heeger model: Polaron excitations and optical absorption

TL;DR

This study extends the Su-Schrieffer-Heeger model to doped C60 and C70 fullerenes, predicting polaron formation, energy level intrusions, and new optical absorption features, with numerical results aligning with known undoped behaviors.

Contribution

The paper introduces an extended model for doped fullerenes, revealing polaron excitations and optical signatures not previously characterized.

Findings

Polarons are predicted in doped C60 and C70.

Doping causes energy level intrusions in the gap.

New optical absorption peaks are identified.

Abstract

We extend the Su-Schrieffer-Heeger model of polyacetylene to C_{60} and C_{70} molecules, and solve numerically. The calculations of the undoped systems agree well with the known results. When the system (C_{60} or C_{70}) is doped with one or two electrons (or holes), the additional charges accumulate almost along an equatorial line of the molecule. The dimerization becomes weaker almost along the same line. Two energy levels intrude largely in the gap. The intrusion is larger in C_{70} than in C_{60}. Therefore, ``polarons'' are predicted in doped buckminster- fullerenes. We calculate optical absorption coefficient for C_{60} in order to look at how ``polarons'' will be observed. It is predicted that there appears a new peak at the lower energy than the intergap transition peaks. It is also found that C_{60} and C_{70} are related mutually with respect to electronical structures as well as lattice geometries. (to be published in Phys. Rev. B 45, June 15 issue)