Path-integral approach to resistivity anomalies in anharmonic systems

Different classes of physical systems with sizeable electron-phonon coupling and lattice distortions present anomalous resistivity behaviors versus temperature. We study a molecular lattice Hamiltonian in which polaronic charge carriers interact with nonlinear potentials provided by local atomic fluctuations between two equilibrium sites. A path-integral model is developed to select the class of atomic oscillations which mainly contributes to the partition function, and the electrical resistivity is computed in a number of representative cases. We argue that the common origin of the observed resistivity anomalies lies in the time retarded nature of the polaronic interactions in the local structural instabilities.