Critical current in cross-whiskers Josephson junctions and mechanism of cuprate superconductivity

Contacting the c planes of two Bi2212 whiskers we made cross-whiskers junctions with intrinsic Josephson junction nature. The cross-angle dependence of the critical current has a fourfold symmetry and therefore the symmetry of the superconducting order parameter is d-wave like. However, the angular dependence is much stronger than that of the conventional d-wave. Recently, neutron scattering experiments in cuprate superconductors showed the occurrence of very large charge fluctuations with relatively low frequencies along the q x and q y axes. Taking account of this fact, we calculated the superconducting order parameter originating from the Coulomb channel and obtained the d-wave like order parameter whose structure is consistent with the present experiments.