COUPLING BETWEEN PLANES AND CHAINS IN YBA2CU3O7 - A POSSIBLE SOLUTIONFOR THE ORDER-PARAMETER CONTROVERSY

We propose to explain the contradictory experiments about the symmetry of the order parameter in YBa2Cu3O7 by taking into account the coupli ng between planes and chains. This leads to an anticrossing of the pla ne and chain band. We include an attractive pairing interaction within the planes and a repulsive one between planes and chains, leading to opposite signs for the order parameter on planes and chains, and to no des of the gap because of the anticrossing. Our model blends s-wave an d d-wave features, providing a natural explanation for all the contrad ictory experiments.