Theory of Macroscopic Quantum Tunneling in High-T_c c-Axis Josephson Junctions

We study macroscopic quantum tunneling (MQT) in c-axis twist Josephson junctions made of high-T_c superconductors in order to clarify the influence of the anisotropic order parameter symmetry (OPS) on MQT. The dependence of the MQT rate on the twist angle γ about the c-axis is calculated by using the functional integral and the bounce method. Due to the d-wave OPS, the γ dependence of standard deviation of the switching current distribution and the crossover temperature from thermal activation to MQT are found to be given by cos2γ and sqrt{cos2γ}, respectively. We also show that a dissipative effect resulting from the nodal quasiparticle excitation on MQT is negligibly small, which is consistent with recent MQT experiments using Bi{}₂Sr{}₂CaCu{}₂O{}_{8 + δ} intrinsic junctions. These results indicate that MQT in c-axis twist junctions becomes a useful experimental tool for testing the OPS of high-T_c materials at low temperature, and suggest high potential of such junctions for qubit applications.