Specific heat study of the Na0.3CoO2· 1.3H2O superconductor: influence of the complex chemistry

Abstract

We report results of specific heat measurements on polycrystalline samples of the layered superconductor, Na 0.3 CoO 2 ⋅1.3H 2 O. The electronic contribution to the specific heat, γ, is found to be 12.2 mJ/mol-K 2 . The feature at the superconducting transition is rather sharp, becoming broad and strongly suppressed in an applied magnetic field. The data indicate a residual normal state electronic specific heat at low temperatures, implying that there is a sizable population of normal state electrons in the samples even below T c . Inhomogeneity in the Na content, to which the superconducting state is exquisitely sensitive, appears to be the most likely explanation for these results. These results further indicate that special sample handling is required for an accurate characterization of the superconducting state in this material.

Magnetic Correlation of NaxCoO2and Successive Phase Transitions of Na0.5CoO2–NMR and Neutron Diffraction Studies–

“…22) In any case, it seems to be important for the complete understanding of the superconductivity of Na 0.3 CoO 2 ⋅yH 2 O, to construct a consistent explanation of various kinds of experimental results. [12][13][14][15][16][17][18][19][20][21][22][23] …”

Evidence of nodal superconductivity inNa0.35CoO2·1.3H2Yang1, Lin2, Sun3 et al. 2005Phys. Rev. B637530View full textAdd to dashboardCite

“…[20][21][22][23][24], and persists with H at least up to 6 T. To further analyze the data, the first step is to quantify the normal state specific heat C n (T). C n can be written as The resultant C n is shown as the solid curve in Fig.…”

Shubnikov–de Haas Effect in the Metallic State ofNa0.3CoO2

“…DOI: 10.1103/PhysRevLett.97.126401 PACS numbers: 71.18.+y, 71.30.+h, 72.15.Gd A number of theoretical treatments have suggested that the nature of the superconducting pairing mechanism in hydrated Na x CoO 2 is unconventional and that it probably corresponds to a spin-triplet state [1][2][3][4]. Nevertheless, the experimental situation remains unclear with heat capacity experiments in the superconducting state suggesting that the electronic contribution can either be described in terms of an order parameter having nodal lines [5], a hypothesis supported by muon spin resonance ( SR) experiments [6], or simply in terms of inhomogeneity in the Na content [7]. Measurements of the 59 Co nuclear magnetic resonance Knight shift supports either spin-triplet [8] or singlet pairing [9].…”

“…Nevertheless, the experimental situation remains unclear with heat capacity experiments in the superconducting state suggesting that the electronic contribution can either be described in terms of an order parameter having nodal lines [5], a hypothesis supported by muon spin resonance ( SR) experiments [6], or simply in terms of inhomogeneity in the Na content [7]. Measurements of the 59 Co nuclear magnetic resonance Knight shift supports either spin-triplet [8] or singlet pairing [9].…”