High-speed flux flow of Josephson vortices in HTS single crystals

Abstract

We have estimated velocities of vortices introduced between the superconducting layers of high-temperature superconductors under a driving current flowing along the c-axis. The measured vortex velocity is approximately 4 m/s in the micro-bridges with typical sizes of 60 micrometer long and 40 X 50 micrometer<SUP>2</SUP> area fabricated from La<SUB>2-x</SUB>Sr<SUB>x</SUB>CuO<SUB>4</SUB> (LSCO) single crystals by the electro-discharge machining (EDM) technique. In the framework of flux creep model can explain that the creep occurs in the bridges with large size causing a low bias current density. On the other hand, we observed a sharp up-turn in flux-flow branches on current-voltage characteristics of the micro-bridges fabricated by the FIB technique, which are smaller than the bridges fabricated by the EDM. This indicates that the motion of Josephson vortices in LSCO matches the propagation of an electromagnetic wave with one of the modes, which corresponds to the mode velocity of 1.6 X 10<SUP>5</SUP> m/s, in the multi-layered structure. The high-speed flux- flow of Josephson vortices can be utilized for high-speed switching gates or electromagnetic wave oscillators in millimeter and sub- millimeter wave bands.