We have used the concept of flux quantization in superconducting rings with 0, 2, and 3 grain-boundary Josephson junctions to test the pairing symmetry in high- 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, has been observed in the 3-junction ring, but not in the 2-junction rings. These results are consistent with -wave pairing symmetry.
- Received 21 March 1994
- Revised 19 May 1994
- Published in the issue dated 25 July 1994
© 1994 The American Physical Society