Orthorhombically Mixed s and d$_{x^2-y^2}$ Wave Superconductivity and Josephson Tunneling

TL;DR

This paper investigates how orthorhombicity affects Josephson tunneling in high-temperature superconductors, highlighting the limitations of twinned crystal experiments in determining the superconducting order parameter symmetry.

Contribution

It clarifies the influence of orthorhombicity on Josephson tunneling and emphasizes the importance of untwinned single crystals for accurately identifying the order parameter symmetry.

Findings

Twinned crystals do not reveal the dominant pairing symmetry.

Experiments on untwinned crystals are necessary for definitive symmetry determination.

Orthorhombicity impacts Josephson tunneling measurements.

Abstract

The effect of orthorhombicity on Josephson tunneling in high T$_c$ superconductors such as YBCO is studied for both single crystals and highly twinned crystals. It is shown that experiments on highly twinned crystals experimentally determine the symmetry of the superconducting twin boundaries (which can be either even or odd with respect to a reflection in the twinning plane). Conversely, Josephson experiments on highly twinned crystals can not experimentally determine whether the superconductivity is predominantly $s$-wave or predominantly $d$-wave. The direct experimental determination of the order-parameter symmetry by Josephson tunneling in YBCO thus comes from the relatively few experiments which have been carried out on untwinned single crystals.