title: Tunnelling system coupled to a harmonic oscillator: an analytical treatment.
abstract: We give an analytical formula in term of continued fraction expansions for the spectral function of a tunnelling electron, coupled to a local lattice oscillation, in a two-site cluster at non-zero temperature. We also study the spectral function of the polaron, a better defined quasi-particle in the anti-adiabatic regime and at sufficiently low temperature. The exact results obtained allow us to look into a wide range of temperature and coupling. Asymptotic results can be obtained directly from the continued fraction expansions in both adiabatic and anti-adiabatic regimes. In the intermediate/strong anti-adiabatic case, in contrast to the usual Lang-Firsov approximation scheme, we found that there is no shrinking of the polaron band as temperature increases. Polaron bandwidth gets broader by temperature effects.
authors.affiliation: Dipartimento di Fisica, Università di Roma La Sapienza, P. A. Moro 2, I-00185 Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Paganelli
authors.forename: S
authors.initials: S
authors.lastname: Ciuchi