Periodic oscillations of Josephson-vortex flow resistance in oxygen-deficient Y Ba 2 Cu 3 O x

We measured the Josephson vortex flow resistance as a function of magnetic field applied parallel to the $ab$ planes using annealed $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ intrinsic Josephson junctions having high anisotropy $(\ensuremath{\sim}40)$ by oxygen content reduction. Periodic oscillations were observed in magnetic fields above $45\char21{}58\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, corresponding to dense-dilute boundary for Josephson vortex lattice. The observed period of oscillations, which agrees well with the increase of one fluxon per two junctions $({H}_{p}={\ensuremath{\Phi}}_{0}∕2Ls)$, may correspond to formation of a triangular lattice of Josephson vortices as has been reported by Ooi et al. for highly anisotropic $(\ensuremath{\geqslant}200)$ Bi-2212 intrinsic Josephson junctions.