Half-integer flux quantum effect in tricrystal Bi₂Sr₂CaCu₂O_8+δ

We have used a scanning SQUID microscope to directly observe the half-integer flux quantum effect, in epitaxial films of Bi2Sr2CaCu2O8+δ, at the meeting point of a tricrystal substrate of SrTiO3 in a geometry chosen to show this effect for a d-wave superconductor. This observation, when considered along with recent photoemission results, proves that the in-plane order parameter for this high-TC cuprate superconductor closely follows dx2-y2 symmetry.