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

TL;DR

This paper investigates how the anisotropic order parameter symmetry in high-T_c superconductor c-axis twist Josephson junctions affects macroscopic quantum tunneling, revealing specific angular dependencies and minimal dissipation effects, with implications for qubit technology.

Contribution

It provides a theoretical analysis of MQT in high-T_c c-axis twist junctions, highlighting the influence of d-wave OPS and demonstrating their potential for qubit applications.

Findings

MQT rate depends on twist angle as cos(2γ)

Crossover temperature scales as sqrt(cos(2γ))

Dissipative effects from nodal quasiparticles are negligible

Abstract

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 $\gamma$ about the c-axis is calculated by using the functional integral and the bounce method. Due to the d-wave OPS, the $\gamma$ dependence of standard deviation of the switching current distribution and the crossover temperature from thermal activation to MQT are found to be given by $\cos2\gamma$ and $\sqrt{\cos2\gamma}$, 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${}_2$Sr${}_2$CaCu${}_2$O${}_{8 + \delta}$ 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.