SPECIFIC-HEAT ANOMALY OF OVERDOPED BI1.8PB0.3SR1.9CUOY

The temperature dependence of the specific heat of Bi1.8Pb0.3SR1.9CuOy samples in the overdoped region has been measured between 1.5 and 8 K . Specific-heat anomalies were observed at T-c in two superconducting samples, while no anomalies were observed in a nonsuperconducting one. The values of Delta C/gamma T-c were quite small in comparison to the BCS value, and the electronic specific heat in the superconducting st ate near T-c exhibited a weak temperature dependence. These findings a re consistent with the impurity effects predicted by the model of d-wa ve superconductors proposed by Sun and Maki. Furthermore, we found tha t the Sommerfeld constant y increases with increasing doped carrier fr om the superconducting region to the normal metal region,in contrast t o the case of La2-xSrxCuO4.