dependence (see Fig. 7). Therefore, the regime σ ≥ σ ∗ for our low-dissipative junctions was realized. Finally, we notice that Eq. (11) describes the averaged value of the amplitude of Fiske resonances. However, as was indicated in Refs. [20, 21], strong mesoscopic fluctuations of various physical values can be observed in inhomogeneous Josephson junctions. These mesoscopic fluctuiations are especially strong for the amplitude of Fiske resonances due to nonlinear character of Eqs. (4) and (5). Therefore, observed deviations of some experimental point from the theoretical curve described by Eq.(11), can be attributed to such mesoscopic fluctuations. This discrepancy could be also due to a possible trapping of a single monopole Abrikosov vortex just near the junction center. The authors thank R. Cristiano, S. Pagano and L. Frunzio for the substantial contribution to the experiment, G. Giuliani and C.Nappi for the helpful theoretical discussion. M. V. F. acknowledges the financial support by SFB 491. The final stage of the preparation of the paper was inspired by the Experiment SUPERGAMMA supported by the Italian Institute of Nuclear Physics (INFN). [1] A. Barone and G.Paterno, Physics and Applications of the Josephson Effect , Wiley, New York, 1982. [2] I. M. Dmitrenko, I. K. Yanson, and V. M. Svistunov, Pis’ma Zh. Eksp. Teor. Fiz. , 2 17 (1965) [ JETP-Letters , 2 10 (1965)]; D. D. Coon and M. D. Fiske, Phys. Rev. , 138 A744 (1965). [3] I. O. Kulik, Pis’ma Zh. Eksp. Teor. Fiz. , 2 134 (1965) [ JETP Letters , 2 84 (1965)]. [4] P. Caputo, M. V. Fistul’ and A. V. Ustinov Phys. Rev. B , 63 214510 (2001). [5] A. V. Ustinov, H. Kohlstedt, M. Cirillo, N. F. Pedersen, G. Hallmanns, and C. Heiden, Phys. Rev. B , 48 10614 (1993). [6] V. M. Krasnov, N. Mros, A. Yurgens, D. Winkler, Phys. Rev. B , 59 8463 (1999). [7] D. Winkler, Y. M. Zhang, P. A. Nilsson, E. A. Stepantsov, and T. Claeson, Phys. Rev. Lett. , 72 1260 (1994). [8] C. Nappi, E. Sarnelli, M. Adamo, M. A. Navacerrada, Phys. Rev. B , 74 144504 (2006). [9] J. Pfeiffer, M. Kemmler, D. Koelle, R. Kleiner, E. Goldobin, M. Weides, A. K. Feofanov, J. 19 Acknowledgments