Fluctuation-assisted transport in polymers

We consider for the first time the explicit role that multi-mode fluctuations play in determining the transport characteristics of inhomogeneous conductors and insulators. Basing ourselves on rigorous analytical and thermodynamic calculations and recent Monte Carlo simulations, we have been able to identify experimentally the novel exp(aTk), k>0, behaviour in the low-temperature transport regime of pyrrole-based polymers. The variable range hopping and fluctuation-assisted granular transport regimes can be clearly differentiated from each other at very low temperatures using different pyrrole compounds. The apparent universality of exp[ - (To/T)s]-type laws can be related to the fact that variable range hopping and variable range tunnelling give rise to similar laws in intermediate temperature regimes. The excitation modes which assist the carriers to cross the barriers at low temperatures can be identified as acoustic phonon modes rather than the charge fluctuation modes invoked in doped polyacetylene.