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Experiments indicating the excitation of whispering gallery type electromagnetic modes by a vortex moving in an annular Josephson junction are reported. At relativistic velocities the Josephson vortex interacts with the modes of the superconducting stripline resonator giving rise to novel resonances on the current-voltage characteristic of the junction. The experimental data are in good agreement with analysis and numerical calculations based on the two-dimensional sine-Gordon model. 74.50.+r, 05.45.Yv, 85.25.Cp, 42.60.Da Whispering gallery modes are universal linear excitations of circular and annular resonators. They have first been observed in form of a sound wave traveling along the outer wall of a walkway in the circular dome of St. Paul's Cathedral in London and were investigated by Lord Rayleigh [1] and others [2]. In the 2 meter wide walkway, which forms a circular gallery of 38 meter diameter about 40 meters above the ground of the cathedral, the whispering of a person can be transmitted along the wall to another person listening to the sound on the other side of the dome. The investigations by Rayleigh led to the conclusion that the whisper of a person does excite acoustic eigenmodes of the circular dome which can be described using high order Bessel functions. This acoustic phenomenon lends its name "whispering gallery mode" to a number of similar, mostly electromagnetic excitations in circular resonators. Whispering gallery modes are of strong interest in micro-resonators used for ultra small lasers [3]. Most recently, circular resonators with small deformations, in which chaotic whispering gallery modes were observed, attracted a lot of attention [4]. Here we describe the experimental observation of electromagnetic whispering gallery modes excited by a vortex moving in an annular Josephson junction of diameter less than 100 µm.A long Josephson junction is an intriguing nonlinear wave propagation medium for the experimental study of the interaction between linear waves and solitons [5]. In this letter we report the excitation of whispering gallery type electromagnetic modes by a topological soliton (Josephson vortex) moving at relativistic velocities in a wide annular Josephson junction. We make use of the same Josephson vortex for both exciting and detecting the whispering gallery mode. These modes are manifested by their resonant interaction with the moving vortex, which results in a novel fine structure on the current-voltage characteristic of the junction. Our experiments are consistent with the recently published theory tion are described by the perturbed sine-Gordon equation (PSGE) for the superconducting phase difference φ between the top and bottom superconducting electrodes of the junction [5]. The Josephson vortex, often also called fluxon, corresponds to a twist over 2π in φ. It carries a magnetic flux equal to the magnetic flux quantum Φ 0 = h/2e = 2.07 10 −15 Vs. Physically, this flux is induced by a vortex of the screening current flowing across the junction barrier. Linear excitatio...

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