Specific Heat Study on Cu_xBa₂Ca₃Cu₄O_y

Abstract

Specific heat anomaly was studied on Cu_xBa₂Ca₃Cu₄O_y. ΔC/T_c, a height of peak of the specific heat at the superconducting transition (T_c) divided by T_c, is less than 60% of that of optimally doped YBa₂Cu₃O_7-δ. This suggests that a large density of states (DOS) remains to prohibit the creation of Bardeen-Cooper-Schrieffer (BCS) pairs at T_c. It is much larger than the residual DOS at 0 K. We interpret that the “missing DOS” start to become BCS pairs at a temperature lower than T_c, as proposed by an NMR study [Phys. Rev. B 61 (2000) 9707], though we have not yet seen clear evidence of this.