Theory of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Cross-Whisker Josephson Junctions

TL;DR

This paper analyzes cross-whisker Josephson junctions in Bi$_2$Sr$_2$CaCu$_2$O$_{8+eta}$, challenging the d-wave symmetry assumption and suggesting coherent c-axis transport in whiskers based on experimental data.

Contribution

It provides a new interpretation of whisker junction data, indicating coherence in c-axis transport and questioning the d-wave order parameter dominance.

Findings

Whisker junction data are unlikely to result from a predominantly d-wave order parameter.

Results suggest coherent c-axis transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+eta}$ whiskers.

Analysis challenges previous interpretations of single crystal junctions.

Abstract

Takano {\it et al.} [Phys. Rev. B {\bf 65}, 140513 (2002) and unpublished] made Josephson junctions from single crystal whiskers of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ crossed an angle $\phi_0$ about the $c$ axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density $J_c(\phi_0)$. Like the single crystal results of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)], we show that the whisker data are unlikely to result from a predominantly d-wave order parameter. However, unlike the single crystals, these results, if correct, require the whisker c-axis transport to be coherent.