Comparison Between The First- And The Second-Junction Switchings In A Small Stack Of Bi2sr2cacu2oy Intrinsic Josephson Junctions

We measured the switching current distributions of the first- and the second-junction switchings in a small stack of Bi2Sr2CaCu2Oy intrinsic Josephson junctions. Switching distribution for the first switching from the zero-voltage state became independent of temperature below 0.8 K suggesting the crossover from thermal activation to macroscopic quantum tunneling. On the other hand, switching distribution for the second switching from the first resistive state showed the similar temperature-independent behavior up to much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of self-heating owing to the dissipative currents after the first switching.