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Switching current distributions and macroscopic quantum tunneling in over-doped BSCCO mesas with nanometer thickness

The current–voltage characteristics and switching dynamics are studied in over-doped (Pb,Bi)2Sr2CaCu2O8+δ (PbBi2212) and Bi2Sr2Ca2Cu3O10+δ (Bi2223) mesa structures containing a few atomic-scale intrinsic Josephson junctions (IJJ) along the c axis. The cleave-in-vacuum method enables us to avoid the contact problems that are always accompanied by mesa structures. The highest critical current density of the zero-voltage state as Jc1 = 3.2 kA cm−2 among our micron-scale mesa structures of BSCCO cuprates are achieved. Narrowing of the switching probability distribution (SPD) due to suppression of the thermal fluctuation tends to saturate at 5 K, which is regarded as a symptom of macroscopic quantum tunneling (MQT). The crossover temperature between the MQT and the thermal escape regions is estimated as 2.2 K for the sample with the highest Jc1. In the high temperature region, another narrowing in SPD is observed that was attributed to the phase retrapping.