c-Axis Twist Bi2Sr2CaCu2O(8+delta) Josephson Junctions: A New Phase-Sensitive Test of Order Parmaeter Symmetry

TL;DR

This paper presents a phase-sensitive test of the order parameter symmetry in Bi2Sr2CaCu2O(8+delta) Josephson junctions, revealing the presence of an s-wave component and incoherent tunneling, challenging previous assumptions about d-wave symmetry.

Contribution

It introduces a new phase-sensitive test using c-axis twist junctions to determine the order parameter symmetry in high-Tc superconductors.

Findings

Critical current density is independent of twist angle near Tc.

Order parameter contains an s-wave component, not d-wave.

C-axis Josephson tunneling is incoherent.

Abstract

Li et al. found that the critical current density JcJ across atomically clean c-axis twist junctions of Bi2Sr2CaCu2O(8+x) is the same as that of the constituent single crystal, JcS, independent of the twist angle phi0, even at Tc. We investigated theoretically if a dx2-y2-wave order parameter might twist by mixing in dxy components, but find that such twisting cannot possibly explain the data near to Tc. Hence, the order parameter contains an s-wave component, but not any dx2-y2-wave component. In addition, the c-axis Josephson tunneling is completely incoherent. We also propose a c-axis junction tricrystal experiment which does not rely upon expensive substrates.