INPLANE PENETRATION-DEPTH ANISOTROPY IN A D-WAVE MODEL

The zero-temperature penetration depth in the CuO2 plane of YBa2Cu3O7 has been found to be very anisotropic. The large measured difference b etween the a and b directions is taken as evidence that a significant part of the condensate resides in the chains. We present a simplified model for this anisotropy in which planes (CuO2) and chains (CuO) are described within a single tight-binding band but with different hoppin g parameters in the a and b directions. The pairing is assumed to be d ue to spin fluctuations in the nearly antiferromagnetic Fermi liquid, but a different mechanism that leads to d-wave-type pairing would have similar results.