No abstract

Transport and thermodynamical properties as well as structural investigations in the well-characterized 90 K-class high-T~ superconductor YBa2Cu307 are presented, especially in relation to the fundamental mechanism of the high-T~ superconductivity. High-precision specific heat measurements around T~ =91.8K reveal that the value of AC/T c is 48 _+ 2 mJ/mol K 2. This value results in the fact that the value of AC/yT~ is 1.33, which is close to 1.43, the weak-coupling BCS value, provided that the coefficient, y, of the linear term in the specific heat is 36 -+ 2 mJ/mol K 2.