Strong coupling, fluctuations and the specific heat of YBa2,Cu3O7-δ

Specific-heat data on the high-temperature superconductor YBa2Cu3O7-delta provide evidence for strong coupling. The data on ceramic and single-crystal samples also indicate that, when there is a fluctuation contribution to the specific-heat anomaly at T(c), the anomaly is reduced in height. These results are consistent with the idea that an oxygen deficiency reduces gamma and enhances fluctuation effects.