PROXIMITY EFFECT AND JOSEPHSON COUPLING IN THE SO(5) THEORY OF HIGH-T-C SUPERCONDUCTIVITY

We consider proximity effect coupling in superconducting-antiferromagn etic-superconducting sandwiches using the recently developed SO(5) eff ective theory of high temperature superconductivity. We find that, for narrow junctions, the A region acts like a strong superconductor, and that there is a critical junction thickness which depends on the effe ctive SO(5) coupling constants and on the phase difference across the junction, at which the A region undergoes a Freedericksz-like transiti on to a state which is intermediate between superconductor and antifer romagnet. For thick junctions, the current-phase relation is sinusoida l, as in standard SNS and SIS junctions, but for thin junctions it sho ws a sharp break in slope at the Freedericksz point.