Direct Experimental Evidence of a Mixed Symmetry of the Order Parameter of YBCO
Abstract
C-axis Josephson tunneling between a conventional superconductor (Pb) and a high Tc superconductor (YBCO) in general only couples to the s-symmetry part of the order parameter of the high Tc superconductor. By fabricating Pb/YBCO Josephson tunnel junctions which overlap a single twin boundary of the YBCO crystal with comparable junction areas in the two twin domains, we have been able to probe the presence of the d-symmetry part of the YBCO order parameter. In the event that the d-component is larger than the s-component, the YBCO order parameter exhibits d+s and d-s symmetry in neighboring twin domains due to phase coherence, resulting in partial or complete cancellation of c-axis Josephson coupling to the Pb in zero magnetic field. This is manifested through the observed minimum at zero field in the I_c(B) pattern. We have measured several of these junctions, and the I_c(B) curves consistently show a zero field minimum in the absence of significant trapped flux. This is in drastic contrast to the Fraunhofer pattern we have previously observed in junctions made either over one single domain or many twin domains of YBCO.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.R1102S