Although initially quite controversial, it has been widely accepted that the Cooper pairs in optimally doped cuprate superconductors have predominantly dx2-y2 wavefunction symmetry. The controversy has now shifted to whether the high-Tc pairing symmetry changes away from optimal doping. Here we present phase-sensitive tricrystal experiments on three cuprate systems: Y0.7Ca0.3Ba2Cu3O7-x (Ca-doped Y-123), La2-xSrxCuO4 (La-214) and Bi2Sr2CaCu2O8+x (Bi-2212),with doping levels covering the underdoped, optimal and overdoped regions. Our work implies that time-reversal invariant, predominantly dx2-y2 pairing symmetry is robust over a large variation in doping, and underscores the important role of on-site Coulomb repulsion in the making of high-temperature superconductivity.
@article{arxiv.cond-mat/0402655,
title = {Robust dx2-y2 pairing symmetry in high-temperature superconductors},
author = {C. C. Tsuei and J. R. Kirtley and G. Hammerl and J. Mannhart and H. Raffy and Z. Z. Li},
journal= {arXiv preprint arXiv:cond-mat/0402655},
year = {2009}
}