Specific-heat of Na0.35CoO2 • 1.3H2O:: Effects of sample age and pair breaking on two-gap superconductivity

Specific-heat measurements on Na0.35CoO2 center dot 1.3H(2)O show an evolution of the superconductivity, and its ultimate disappearance, with increasing sample age. An increase in pair breaking action, which occurs preferentially in an electron band with a small energy-gap, produces a shift in the relative contributions of two electron bands to the superconducting condensation. The similarity of the time scale for these changes to that recently reported for structural changes suggests a relation between the two effects and a basis for understanding the sample dependence of the properties of this material in general. Published by Elsevier B.V.