Collective Josephson vortex dynamics in a finite number of stacked intrinsic Josephson junctions

摘要

We report the experimental confirmation of the collective transverse plasma modes excited by the Josephson vortex lattice in stacks of intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_(8+x) single crystals. The excitation was confirmed by analyzing the temperature (T) and magnetic-field (H) dependencies of the multiple sub-branches in the Josephson vortex-flow region of the current-voltage characteristics of the system. In the near-static Josephson vortex state for a low tunneling bias current, pronounced magnetoresistance oscillations were observed, which represented a triangular-lattice vortex configuration along the c axis. In the dynamic vortex state in a sufficiently high magnetic field and for a high-bias current, splitting of a single Josephson vortex-flow branch into multiple sub-branches was observed. Detailed examination of the sub-branches for varying H field reveals that sub-branches represent the different modes of the Josephson vortex lattice along the c axis, with varied configuration from a triangular to a rectangular lattice. These multiple sub-branches merge to a single curve at a characteristic temperature, above which no dynamical structural transitions of the Josephson vortex lattice is expected.