Josephson lattice structure in mesoscopic intrinsic Josephson junctions by means of flux-flow resistance in Bi₂Sr₂CaCu₂O_{8+δ}

Dynamical nature of the Josephson vortex (JV) system in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) has been investigated in the presence of the c-axis current with magnetic field alignments very close to the $ab$-plane. As a function of magnetic fields, the c-axis JV flux flow resistance oscillates periodically in accordance with the proposed JV triangular structure. We observe that this oscillating period becomes doubled above a certain field, indicating the structure transition from triangle to square structure. This transition field becomes lower in junctions with smaller width perpendicular to the external field. We interpret that this phenomena as the effect of the edge deformation of the JV lattice due to surface current of intrinsic Josephson junctions as pointed by Koshelev.