The effects of dimensionality on small-polaron motion have been studied in the framework of the Holstein model in which the intermolecular forces act through a first-neighbors pair potential. A perturbative approach allows one to calculate the matrix elements determining both the polaronic band and the site-jump hopping probability as a function of temperature. It is found that the crossover temperature Td* between bandlike and diffusive motion is sensibly reduced in low-dimensional systems due to the enhanced importance of the off-diagonal scattering processes. By increasing the polaron binding energy the bandwidth narrows and the hopping probability quickly drops, hence Td* is shifted upwards. It is shown that the dispersion in the phonon spectrum is essential for the validity of the model.
Two- and three-dimensional polaronic motion: Beyond the Holstein model
ZOLI, Marco
1998-01-01
Abstract
The effects of dimensionality on small-polaron motion have been studied in the framework of the Holstein model in which the intermolecular forces act through a first-neighbors pair potential. A perturbative approach allows one to calculate the matrix elements determining both the polaronic band and the site-jump hopping probability as a function of temperature. It is found that the crossover temperature Td* between bandlike and diffusive motion is sensibly reduced in low-dimensional systems due to the enhanced importance of the off-diagonal scattering processes. By increasing the polaron binding energy the bandwidth narrows and the hopping probability quickly drops, hence Td* is shifted upwards. It is shown that the dispersion in the phonon spectrum is essential for the validity of the model.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
