Bi2Sr2CaCu2O8+δ c-axis bicrystal twist Josephson junctions: the superior phase-sensitive test of order parameter symmetry

Extensive atomic resolution transmission electron microscopy and holography studies showed the c-axis bicrystal twist junctions of Bi2Sr2CaCu2O8+δ (Bi2212) studied by Li et al. [Phys. Rev. Lett. 83 (1999) 4160] to be atomically clean, with electronic and elastic properties independent of the twist angle. These critical current experiments thus provide prima facie evidence for a dominant s-wave order parameter and strongly incoherent c-axis quasiparticle tunnelling in Bi2212. New Bi2212 cross-whisker junction data confirming the Li et al. experiment are presented.