Evidence of two-gap s-wave superconductivity in YBa2Cu3O7-x from microwave surface impedance measurements.

Epitaxial thin films of YBa[sub 2]Cu[sub 3]O[sub 7[minus][ital x]] with low cation and oxygen disorder exhibit two features in the temperature dependence of the microwave surface impedence which are consistent with a weak [ital s]-wave superconducting state associated with the CuO chains. First, both the microwave surface resistance and the magnetic field penetration depth exhibit a weak exponential temperature dependence below 30 K corresponding to an energy gap of about 6 meV. Second, the penetration depth exhibits a small bump at about 60 K, which is consistent with a two-band BCS calculation using 6 meV for the smaller gap.