Polaronic effects in disordered dielectrics

Abstract

A number of experimental techniques for distinguishing small-polaronic hops from nonpolaronic hops in disordered dielectrics are presented. It is shown that the temperature and field dependencies of DC conductivity provide an indication of the small-polaronic (ultrasmall polarons) hops. For small-polaronic hops, a field dependence of DC conductivity exhibits a section where /spl sigma/ decreases with E prior to exponential increase in /spl sigma/. In the case of substances with ultrasmall polarons the temperature dependence of the electrical conductivity can be represented in the form ln (/spl sigma/T/sup 3/2/)/spl sim/T. The strong field polaronic effects take place in the lower frequency range up to boundary frequency which temperature dependence is determined by electron-lattice coupling strength. These results are in accord with observations in amorphous tantalum oxide for which there is explicit evidence of small-polaronic hopping.