Anisotropy dependence of Josephson-vortex flow resistance

Periodic oscillations of the Josephson-vortex flow resistance as a function of parallel magnetic field have been observed when Josephson vortices form a triangular lattice. Depending on the applied current and sample size, the period of oscillations has been found to double above a particular magnetic field H2s. In order to investigate how H2s depends on the anisotropy of the sample, we have measured the vortex-flow resistance as a function of parallel magnetic field for an underdoped Bi2Sr2CaCu2O8+y (Bi-2212) single crystal whose anisotropy was controlled by annealing. We have found that H2s increases systematically with decreasing anisotropy. This behavior is qualitatively consistent with the theoretical expectation that H2s is inversely proportional to the square of the anisotropy parameter γ.