Theory of Bi₂Sr₂CaCu₂O₈₊δ Cross-Whisker Josephson Junctions

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Takano et al. [Phys. Rev. B 65, 140513 (2002) and unpublished] made Josephson junctions from single crystal whiskers of Bi₂Sr₂CaCu₂O₈₊δ crossed an angle ϕ₀ about the c axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density Jc(ϕ₀). Like the single crystal results of Li et al. [Phys. Rev. Lett. 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.