IN PLANE ANISOTROPY IN OPTIMALLY DOPED YBA2CU3O6.95

Single crystals untwinned optimally doped YBa2Cu3O9.65 show a large de gree of anisotropy in a-b plane properties such as resistivity, infrar ed conductivity and value of zero temperature penetration depth. This source of orthorhombicity must ultimately reside in the CuO chains. Us ing a three plane model; 2 CuO2 and one CuO (chain plane), we study so lutions of three coupled BCS equations which include inter- as well as intra-plane coupling. The gaps are found to contain s- as well as d-w ave symmetries. From our solutions, we calculate the penetration depth and compare with experiments.