Tricrystal tunneling evidence for d-wave pairing symmetry in cuprate superconductors

Strong evidence for d-wave pairing symmetry in high-temperature superconductors such as YBa2Cu3O7 and Tl2Ba2CuO6+δ has been obtained by monitoring the presence or absence of the half-integer flux quantum effect in various controlled - orientation tricrystal superconducting systems. New results of a tricrystal tunneling experiment with Gd Ba2Cu3O7 will also be presented.