Specific heat study on CuxBa2Can-1CunOy

Two "superconducting transition temperatures" (T(c)s) of CuxBa2CaCu4Oy. wer e examined by the specific heat measurement. Comparing the specific heat un der magnetic field (14 T) and that without field, two anomalies were observ ed in the electronic specific heat. When there are more than two Fermi surf aces (FSs) and the superconducting gaps do not develop simultaneously in th ese FSs, we can expect two anomalies. Strictly speaking the second anomaly at lower temperature (T-c2) is not due to the real phase transition but its vestige. A theoretical inspection indicates the second anomaly means the i nter-FS interaction is very weak. If the symmetry of the superconducting ga p on one FS is different from that on the other. one can expect a drastic s uppression of the inter-FS interaction. (C) 2001 Elsevier Science B.V. All rights reserved.