DC AND AC CONDUCTIVITY IN HOPPING ELECTRONIC SYSTEMS

The various theories of dc and ac conductivity in materials with hopping electronic charge carriers are critically examined in the light of the available experimental evidence. The temperature dependence of the dc conductivity suggests that in most materials the transition from nearest-neighbour hopping to variable-range hopping has been observed. However the theory in this region is insufficiently developed to enable meaningful determinations of the relevant parameters to be made from experimental data. The situation with ac theory is even less satisfactory, none of the existing theories being capable of accounting adequately for the observed behaviour. Neglect of many-body interactions and of the effect of the dielectric lattice, in addition to that of the charge carriers, are seen as the principal shortcomings. It follows, then, that the question of any relationship between the dc and ac conductivities cannot be answered at present, because of the lack of reliable data and because of insufficient theoretical understanding of the carrier processes in question. © 1979.