Josephson tunneling in high-$T_c$ superconductors

TL;DR

This paper investigates Josephson tunneling in high-$T_c$ superconductors, focusing on symmetry-breaking states, crystal orientations, and experimental evidence to distinguish pairing symmetries in YBCO.

Contribution

It introduces a macroscopic invariance group framework for twinned crystals and proposes a ring geometry method to differentiate $s$-wave and $d_{x^2-y^2}$-wave symmetries.

Findings

Comparison of tunneling from time-reversal symmetry-breaking and invariant states.

Framework for analyzing twinned crystal superconducting states.

Experimental evidence supporting orthorhombic $ux^2+vy^2$ symmetry in YBCO.

Abstract

This article describes the Josephson tunneling from time-reversal symmetry-breaking states and compares it with that from time-reversal invariant states for both twinned and untwinned crystals and for both $c$-axis and basal-plane currents, in a model for orthorhombic YBCO. A macroscopic invariance group describing the superconducting state of a twinned crystal is introduced and shown to provide a useful framework for the discussion of the results for twinned crystals. In addition, a ring geometry, which allows $s$-wave and $d_{x^2-y^2}$-wave superconductivity in a tetragonal superconductor to be distinguished on the basis of symmetry arguments only, is proposed and analyzed. Finally, an appendix gives details of the experimental Josephson tunneling evidence for a superconducting state of orthorhombic $ux^2+vy^2$ symmetry in YBCO.