Theory of Bi2Sr2CaCu2O8+delta cross-whisker Josephson junctions

Takano et al. [Phys. Rev. B 65, 140513 (2002); J. Low Temp. Phys. 131. 533 (2003)] made Josephson junctions from single crystal whiskers of Bi 2 Sr 2 CaCu 2 O 8 + δ crossed an angle Φ 0 about the c axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density J c (Φ 0 ). As with 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.