Comprehensive low-temperature specific-heat data C(T,H) of Na 0.35CoO 2 · 1.3 H 2O 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 γ n = 13.94 mJ/mol K 2 and Debye temperature Θ D = 362 K are reported. At zero field, a very sharp superconducting anomaly was observed at T c=4.5 K with ΔC/γ nsT 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, δγ(H) ∝ H 1/2, which is also a manifestation of the line nodes. The behaviors of both T C(H) and γ(H) suggest the anisotropy of H c2, or possible crossovers or transitions occurring in the mixed state.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 1 Jan 2005|