Pure d-wave pairing symmetry in high-T_c cuprate superconductors

We have directly observed the half-integer flux quantum effect in controlled-orientation tricrystal Bi2Sr2CaCu2O8+x (Bi2212) and tetracrystal Tl2Ba2CuO6+δ (Tl2201) by using a high-resolution scanning SQUID microscope. The results of these phase-sensitive pairing symmetry tests, along with the recent ARPES data for Bi2212 by Ding et al., have definitively established the existence of pure dx2-y2 - wave pairing symmetry in both Bi2212 and Tl2201. © 1998 Elsevier Science Ltd. All rights reserved.