Pairing symmetry in Bi₂Sr₂Ca₁Cu ₂O_8+x

Although the pairing symmetry of the high-T_c superconductors is widely accepted to be d_x2-y2, measurements in apparent contradiction with this picture have been reported in Bi₂Sr₂Ca ₁Cu₂O_8+x and attributed to s-wave symmetry or complex mixtures of s-wave and d-wave. To clarify this issue, we have measured the transport properties of asymmetric 45° [100]/[110] Bi₂Sr ₂Ca₁Cu₂O_8+x bicrystal Josephson junctions, a geometry sensitive to the pairing symmetry. All samples investigated show complicated but polarity-symmetric modulation of their critical currents with magnetic field, providing unambiguous, clear evidence for a pre-dominant d_x2-y2 pairing symmetry at Bi₂Sr ₂Ca₁Cu₂O_8+x interfaces.