Bi2Sr2CaCu2O8+delta c-axis twist Josephson junctions: A new phase-sensitive test of order parameter symmetry

Li et al. found that the critical current density J(c)(J) across atomically clean c-axis twist junctions of Bi2Sr2CaCu2O8+delta is the same as that of the constituent single crystal, J(c)(S), independent of the twist angle ph i(o), even. at and below T-c. We investigated theoretically if a d(x)2(-y)2 -wave order parameter might twist by mixing in d(xy)-wave components, but f ound that such mixing cannot possibly explain the data near to T-c. Combine d with group theoretical arguments, we then conclude that the order paramet er contains at feast a substantial s-wave component, but does not contain a ny purported d(x)2(-y)2-wave component, except possibly below a second, uno bserved phase transition. By studying tunneling models, we further conclude that the intrinsic c-axis Josephson tunneling in Bi2Sr2CaCu2O8+delta is li kely to be mostly incoherent.