Browsing by Author "Sakurai, H"

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Evidence of nodal superconductivity in Na0.35CoO2 center dot 1.3 H2O: A specific-heat study
(2005-01-01)
Yang, HD
;
Lin, JY
;
Sun, CP
;
Kang, YC
;
Huang, CL
Comprehensive low-temperature specific-heat data C(T,H) of Na0.35CoO2.1.3 H2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. In the normal state, the values of gamma(n)=13.94 mJ/mol K-2 and Debye temperature Theta(D)=362 K are reported. At zero field, a very sharp superconducting anomaly was observed at T-c=4.5 K with DeltaC/gamma(ns)T(c)=1.45 if the specific-heat jump is normalized to the superconducting volume fraction, which is estimated to be 47.4% based on the consideration of entropy balance at T-c for the second-order superconducting phase transition. In the superconducting state, the electronic contribution C-es at H=0 can be well described by the model of the line nodal order parameter. In low H, deltagamma(H)proportional toH(1/2), which is also a manifestation of the line nodes. The behaviors of both T-c(H) and gamma(H) suggest the anisotropy of H-c2, or possible crossovers or transitions occurring in the mixed state.
Various analyses of specific heat for the order parameter of superconductor Na(0.35)coO(2) center dot 1.3H(2)O
(2006-05-01)
Sun, CP
;
Lin, JY
;
Kang, YC
;
Huang, CL
;
Takada, K
Low-temperature specific-heat data C(T) of two Na0.35CoO2. 1.3H(2)O samples (I and II) with temperature T down to 0.6 K without and with magnetic field of 8T are presented. The normal-state linear coefficient of specific heat gamma(n) Debye temperature Theta D, superconducting transition temperature T-c, specific heat jump at T-c, Delta C/T-gamma ns(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 Na0.35CoO2. 1.3H(2)O. (c) 2006 Elsevier B.V. All rights reserved.