Boundary between coherent and noncoherent small polaron motion: Influence of the phonon hardening

The transition from band to hopping conductivity of small polaron is examined within Holstein's molecular crystal model. The conditions under which each of these mechanisms prevail are formulated in terms of the values of the coupling constant S and adiabatic parameter B. Particular attention was paid to the possible influence of the polaron induced modification of phonon spectrum. (C) 2008 Elsevier B.V. All rights reserved.