Study of macroscopic quantum tunnelling inBi2Sr2CaCu2O8+δ intrinsic Josephson junctions

Abstract

We report an experimental observation of the macroscopic quantum tunnelling (MQT) in ad-wave high-temperature superconductor (HTSC)Bi2Sr2CaCu2O8+δ intrinsic Josephson junction (IJJs). It is well known that the current-biased Josephsontunnel junction provides an ideal stage for studying a variety of macroscopicquantum phenomena such as MQT. They have been studied and observed inlow-temperature superconductor (LTSC) Josephson junctions since the early 1980s andhave been established well by now. On the other hand, in the case of HTSC thed-wave pairing symmetry allows for dissipative quasiparticle excitations within thesuperconducting energy gap, which is expected to severely interfere with an observation ofMQT. Contrary to this naive conception, our experimental results have explained that theeffects of the nodal quasiparticles are not strong enough to obscure the observation of theMQT. Furthermore, we found that the MQT in IJJs was observed at approximately 1 K,which was ten times higher than that of LTSC Josephson junctions. This higherclassical-to-quantum crossover temperature is due to their high plasma frequency. We alsodiscuss the resonant activation of IJJs in the presence of microwave radiation.