Polaron Mass and Electron-Phonon Correlations in the Holstein Model

Abstract EN

The Holstein Molecular Crystal Model is investigated by a strong coupling perturbative method which, unlike the standard Lang-Firsov approach, accounts for retardation effects due to the spreading of the polaron size.

The effective mass is calculated to the second perturbative order in any lattice dimensionality for a broad range of (anti)adiabatic regimes and electron-phonon couplings.

The crossover from a large to a small polaron state is found in all dimensionalities for adiabatic and intermediate adiabatic regimes.

The phonon dispersion largely smoothes such crossover which is signalled by polaron mass enhancement and on-site localization of the correlation function.

The notion of self-trapping together with the conditions for the existence of light polarons, mainly in two- and three-dimensions, is discussed.

By the imaginary time path integral formalism I show how nonlocal electron-phonon correlations, due to dispersive phonons, renormalize downwards the e-ph coupling justifying the possibility for light and essentially small 2D Holstein polarons.