Zero-field "Fiske" steps in small Josephson junctions

The theory of Fiske steps in Josephson tunnel junctions is extended to include the presence of structural fluctuations in the barrier. The possibility of excitation of zero-field steps in this case, is discussed. Experimental evidence for the occurrence of zero-field resonances, due to both regular and randomly distributed nonuniformities in "small" Josephson junctions, is reported.