Macroscopic Symmetry Group Describes Josephson Tunneling in Twinned Crystals

TL;DR

This paper introduces a macroscopic symmetry group model for the superconducting state in twinned YBCO crystals, linking twin boundary symmetry to Josephson tunneling experiments and vortex stability.

Contribution

It presents a new macroscopic symmetry group framework for understanding Josephson tunneling in twinned crystals, connecting boundary symmetry to experimental observations.

Findings

Different twin boundary symmetries correspond to distinct macroscopic symmetry groups.

Josephson tunneling experiments can determine the twin boundary symmetry.

Odd-symmetry twin boundaries stabilize vortices with half flux quantum.

Abstract

A macroscopic symmetry group describing the superconducting state of an orthorhombically twinned crystal of YBCO is introduced. This macroscopic symmetry group is different for different symmetries of twin boundaries. Josephson tunneling experiments performed on twinned crystals of YBCO determine this macroscopic symmetry group and hence determine the twin boundary symmetry (but do not experimentally determine whether the microscopic order parameter is primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in YBCO is the stability of vortices containing one half an elementary flux quantum at the intersection of a twin boundary and certain grain boundaries.