Macroscopic quantum tunneling in d-wave high-TC superconductor

We report the first successful observation of the macroscopic quantum tunneling (MQT) in $d$-wave high-$T_{C}$ superconductor (HTSC). Although, MQT, i.e. the quantum mechanical tunneling of the phase variable of the macroscopic wave function through the potential barrier of a Josephson junction, has been observed at around 300 mK in a conventional $s$-wave low-$T_{C}$ superconductor, it has appeared at approximately 1 K in HTSC because of its higher plasma frequency. On the other hand the $d$-wave pairing symmetry, the other hallmark of HTSC, allows for dissipative quasiparticles excitations within the superconducting energy gap, which may severely interfere with the occurrence of MQT. We also show a feasibility of MQT in spite of an existence of the dissipative quasiparticles.