COMMENSURATE FLUXON STATES IN LONG JOSEPHSON-JUNCTIONS WITH INHOMOGENEITIES

Measurements of the dependence of the critical current I(c) on the ext ernal magnetic field H in long Josephson junctions with a periodic lat tice of inhomogeneities are presented. Commensurability between the la ttice of inhomogeneities and the chain of fluxons induces equidistant peaks in the I(c)(H)-curve. Some of these commensurability peaks are f ound to be suppressed as predicted by the theory of Fehrenbacher et al . which takes into account the finite width of the inhomogeneities. Th e suppression of the I(c) peaks takes place when the width of each inh omogeneity is equal to or a multiple of the spacing between the fluxon s in the junction. Together with the suppression of the integer (harmo nic) peaks predicted by theory, experimentally a suppression of subhar monic peaks is also observed. A qualitative explanation of this new ef fect is suggested.