**1. Introduction**

262 Superconductors – Materials, Properties and Applications

1993), pp. 2134-2137, ISSN 0031-9007

Wollman, D. A.; Van Harlingen, D. J.; Lee, W. C.; Ginsberg, D. M. & Leggett, A. J. (1993). Experimental Determination of the Superconducting Pairing State in YBCO from the phase coherence of YBCO-Pb dc SQUIDs. *Phys. Rev. Lett.,* Vol.71, No.13, (September
