paper

Electron--Vibron Interactions and Berry Phases in Charged Buckminsterfullerene: Part I

arXiv:cond-mat/9312074 · doi:10.1103/PhysRevB.49.12998

Abstract

A simple model for electron-vibron interactions on charged buckminsterfullerene C, , is solved both at weak and strong couplings. We consider a single vibrational multiplet interacting with electrons. At strong coupling the semiclassical dynamical Jahn-Teller theory is valid. The Jahn-Teller distortions are unimodal for =1,2,4,5 electrons, and bimodal for 3 electrons. The distortions are quantized as rigid body pseudo--rotators which are subject to geometrical Berry phases. These impose ground state degeneracies and dramatically change zero point energies. Exact diagonalization shows that the semiclassical level degeneracies and ordering survive well into the weak coupling regime. At weak coupling, we discover an enhancement factor of for the pair binding energies over their classical values. This has potentially important implications for superconductivity in fullerides, and demonstrates the shortcoming of Migdal--Eliashberg theory for molecular crystals.

29 pages (+7 figures, 3 available upon request), LATEX, report-number: BM5154

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