  In this article, we wish to give a historical and personal account of the
advent of our tricrystal phase-sensitive symmetry experiments using scanning
SQUID microscope for establishing d-wave pairing symmetry in the cuprate
superconductors. On the occasion of commemorating the 100th anniversary of the
discovery of superconductivity by Kamerlingh Onnes, we are honored to present
this article as part of the Jubilee Celebration.
