Dynamics of Phase Switch in the Intrinsic Josephson Junctions Made of Bi2212 with Perfectly-stoichiometric Cation Compositions

We study the phase switching dynamics in the intrinsic Josephson junctions (IJJs) of Bi₂Sr₂CaCu₂O_y (Bi2212) cuprate superconductors, focusing on the effect of stoichiometry of cation composition. The current-voltage characteristics for the IJJs with the cation composition approaching to be perfectly stoichiometric (Bi:Sr:Ca:Cu=2:2:1:2) show the highly-underdamped nature with a very small retrapping current. We found that the switching current distribution P(I) for the IJJs with perfectly stoichiometric composition and less damage had double peaks or broadened. This suggests that the phase switched junction is not always specified in the case of IJJs with stoichiometric composition, since more than one junction with almost the same switching current is associated with the observed switching events. We obtained the magnitude of a critical current density J _c and an effective temperature T _esc for the phase escape composed of a single component, by analysing the bias current dependence of the switching rate Γ(I). The results indicate that the perfectly-stoichiometric cation composition can greatly enhance the magnitude of J _c, although a crossover temperature to the macroscopic quantum tunnelling (MQT) for the higher-ordered phase switches is not influenced by the enhancement of J _c, in contrast to the conventional MQT theory. (paper)