Pairing Symmetry and Flux Quantization in a Tricrystal Superconducting Ring of YBa2Cu3O7-δ

We have used the concept of flux quantization in superconducting YBa2Cu3O7-δ rings with 0, 2, and 3 grain-boundary Josephson junctions to test the pairing symmetry in high-Tc superconductors. The magnetic flux threading these rings at 4.2 K is measured by employing a scanning superconducting quantum interference device microscope. Spontaneous magnetization of a half magnetic flux quantum, Φ02=h4e has been observed in the 3-junction ring, but not in the 2-junction rings. These results are consistent with d-wave pairing symmetry. © 1994 The American Physical Society.