Excitation of plasma oscillations by moving Josephson vortices in layered superconductors

Electric and magnetic fields created by moving uniform lattice of Josephson vortices in the magnetic field parallel to the layers are calculated in the frame of exactly solvable model. At large velocities of the vortex lattice the plasma oscillations of superconducting electrons are excited by vortex motion, this results in interference features in I-V curves at low temperatures. The spectrum of electromagnetic radiation by moving vortices contains peaks related to the excitation of plasmons and to the Cherenkov radiation. It is known that in high-T c superconductors there exist low-damping plasma oscillations [1]-[7] in the range of hundreds megahertz-terahertz. The presence of an underdamped eigenmode leads to a resonance behavior of the driven modes when frequency and wave-vector of the driven force are close to those of the eigenmode. In particular, frequencies of the electromagnetic field of sliding lattice of Josephson vortices created by magnetic field parallel to the layers can enter the range of plasma modes if the lattice is moving fast enough. The velocity of such vortices driven by transport current perpendicular to the layers may be very large, because the amplitude of the order parameter ∆ inside Josephson vortices is perturbed very slightly. Thus, at large enough voltages across the superconductor the resonance conditions can be satisfied. This results in the generation of plasma oscillations and influences the I-V curves. Below we study the motion of uniform lattice of Josephson vortices in an infinite crystal in magnetic field which is small enough, so that non-linear cores of the vortices do not overlap. We assume that the characteristic frequencies of the problem are small in comparison to ∆. In the presence of vortices the spectrum of the eigenmodes is different from the zero-field spectrum due to oscillations of vortex displacements leading to the sound-like [1],[7],[8] spectrum of the modes. In contrast, the response of a superconductor to the motion of the vortex lattice driven by the transport current calculated in our study, is not related to the oscillations of the vortices, driven modes being related to the plasmons with the plasma edge.