Tricrystal experiments for testing pairing symmetry in cuprate superconductors

Based on macroscopic quantum coherence effects arising from pair tunneling and flux quantization, a series of tricrystal experiments have been designed and carried out to probe the microscopic phase of the pair wavefunction in high-T-c cuprate superconductors. By using a high-resolution scanning SQUID microscope, and the half-integer flux quantum effect in various tricrystal geometrical configurations, we have proven that the order parameter in YBa2Cu3O7 has nodes and lobes consistent with d-wave but not with the g-wave pairing symmetry.