Linear temperature variation of the penetration depth in YB2Cu3O7-delta thin films

We have measured the penetration depth lambda(T) on YBa2Cu3O7 thin films from transmission at 120, 330 and 510 GHz, between 5 and 50 K. Our data yield simultaneously the absolute value and the temperature dependence of lambda(T). In high-quality films lambda(T) exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and lambda(O) = 1570 Angstrom. In a lower quality one, the more usual T-2-dependence is found, and lambda(O) = 3400 Angstrom. This suggests that the T-2 variations is of extrinsic origin. Our results put the d-wave-like interpretation in a much better position.