Av. Ustinov et al., COUPLED FLUXON MODES IN STACKED NB ALOX/NB LONG JOSEPHSON-JUNCTIONS/, Physical review. B, Condensed matter, 48(14), 1993, pp. 10614-10617
The current-voltage characteristics of N vertically stacked Nb-based l
ong Josephson junctions (N = 1, 2, 3) are measured. For a single junct
ion in the stack, we observe the splitting of the flux-flow mode into
M modes, each of them being characterized by different magnetic field
dependence and by different cavity-resonance (Fiske-mode) frequency. O
ur results suggest that a fluxon moving in one junction in the stack m
ay experience M = N different Swihart velocities due to the coupling t
o adjacent junction(s) through the common electrode(s) of the thicknes
s smaller than the London penetration depth. In the twofold stacks, we
find an indication for a coherent mode corresponding to coupled fluxo
n arrays moving in both junctions.