SPECIFIC HEAT IN MONO-CRYSTAL YBCO: λ-LIKE ANOMALIES AT 90K AND 229K

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Abstract
The specific heat, C p , has been measured with high precision in a mono-crystal of YBa 2 Cu 3 O 7−δ (YBCO) superconductor in the temperature range 55K-300K. The measurements provide data with a relative resolution Δ C p / C p of approximately 5 · 10−4. The main conclusions are: 1) Close to the superconducting transition the specific heat shows influence of fluctuations. 2) A reversible second order or weakly first order phase transition is found to occur at T o = 229 K .