Robust d_x2-y2 pairing symmetry in hole-doped cuprate superconductors

The predominant dx2-y2 pairing symmetry in hole-doped cuprate superconductors was investigated. It was shown that Cooper pairs in optimally doped superconductors have wave function symmetry. The controversy whether the pairing symmetry changes away from optimal doping was also investigated. Phase-sensitive tricrystal experiments on three cuprate systems were presented with doping levels covering the underdoped, optimal and overdoped regions.