Order Parameter Symmetry and Unconventional Superconductivity of Na0.30CoO2⋅ 1.3H2O Discussed from Experimental Results

Abstract

An unconventional superconductor of Na0.30CoO2⋅1.3H2O has been reviewed in view of its order parameter symmetry mainly from experimental results for this compound. This superconductor exhibits the ground state (a low field regime) that possesses singlet superconductivity (the s-wave) formed from various elemental order parameter symmetries, spin fluctuations within the C o O 2 plane, and other physical properties, which are proved with comparing these experimental results with theoretical results in this field, and the order parameter symmetry can be identified as the extended s-wave. On the other hand, in the high field regime, triplet superconductivity has been detected by temperature dependence of upper critical fields (H c2(T)) and that of Knight shift as well as the ground state. The triplet superconductivity is understood through Hund’s coupling, hyperfine coupling interaction, Nagaoka ferromagnetism, and the averaged valence of the Co ions in the CoO2. The superconductivity is discussed using the various physical properties which influence the order parameter symmetry of this superconductor, and it also suggested that some quantum phase transitions can be detected with respect to superconductivity of title compounds.