J. He, J.Z. Sun, et al.
Journal of Applied Physics
RECENT discussions of the mechanism of high-temperature superconductivity have focused on the symmetry of the superconducting order parameter (the wavefunction of the superconducting state) as a means of constraining the nature of the interaction that forms the Cooper pairs1, 2. There have been many attempts to measure the symmetry of this parameter in the high-temperature superconductor YBa2Cu3O7 - δ (refs 3–10), but they have not yielded consistent results. Here we show that half-integer flux quantization in superconducting rings with three grain-boundary Josephson junctions, which formed the basis of an earlier, less conclusive symmetry test3, can be used to place firm constraints on the pairing symmetry. For the case of YBa2Cu3O7 - δ, we find that the sign of the order parameter is clearly direction dependent (consistent with a dx2-y2 symmetry) and that the contribution from any out-of-phase isotropic component is less than about 3%. © 1995 Nature Publishing Group.
J. He, J.Z. Sun, et al.
Journal of Applied Physics
L. Krusin-Elbaum, D. López, et al.
Physica C: Superconductivity and its Applications
A.G. Schrott, K.N. Tu, et al.
Physical Review B
J.R. Kirtley, C.C. Tsuei, et al.
Physical Review B - CMMP