Various analyses of specific heat for the order parameter of superconductor Na 0.35coO 2·1.3H 2O

Abstract

Low-temperature specific-heat data C( T) of two Na 0.35CoO 2. 1.3H 2O samples (I and II) with temperature T down to 0.6 K without and with magnetic field of 8 T are presented. The normal-state linear coefficient of specific heat γ n, Debye temperature Θ D, superconducting transition temperature T c, specific heat jump at T c, Δ C/γ nsT c, and superconducting volume of fraction (SVF) are 14.89 mJ/mol K 2, 503, 4.7 K, 1.96, and 26.6% for sample I and 13.94 mJ/mol K 2, 362, 4.5 K, 1.45, and 47.4% for sample II, respectively. Because the superconducting properties may depend on the water content of sample, it is found that the better quality (higher SVF) of sample, the nodal order parameter is better than BCS isotropic s-wave model in describing the gap function of this interesting compound Na 0.35CoO 2. 1.3H 2O.