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Evidence of nodal superconductivity in Na_0.35CoO2-1.3H_2O: a specific heat study

H. D. Yang·J. -Y. Lin·C. P. Sun·Y. C. Kang·C. L. Huang·K. Takada·T. Sasaki·H. Sakurai·E. Takayama-Muromachi
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Abstract

Comprehensive low-temperature specific heat data C(T,H) of Na_0.35CoO2-1.3H_2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. For the normal state, the values of gamma_n=13.94 mJ/mol K2, and Debye temperature 362 K are reported. At zero field, a very sharp superconducting anomaly was observed at Tc=4.5 K with DeltaC/gamma_nTc=1.45. The superconducting volume fraction is estimated to be 47.4 % based on the consideration of entropy balance at Tc 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, gamma(H) H^1/2 which is also a manifestation of the line nodes. The behaviors of both Tc(H) and gamma(H) suggest the anisotropy of Hc2 or possible crossovers or transitions occurring in the mixed state.

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H. D. Yang, J. -Y. Lin, C. P. Sun, Y. C. Kang, C. L. Huang, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi. 2005-02-16. Evidence of nodal superconductivity in Na_0.35CoO2-1.3H_2O: a specific heat study. https://doi.org/10.1103/physrevb.71.020504

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