Competition between Superconductivity and Charge-density Wave Order in Na 0.3 CoO 2 ⋅1.3H 2 O

Three samples of Na 0.3 CoO 2 ⋅1.3H 2 O that differed in sample age showed different ordering: after three and five days, superconductivity with T c ∼4.5 K but different superconducting condensates; after 40 days, no superconductivity but charge-density wave order at T CDW ∼7 K. A pair-breaking action that progresses with sample age and acts preferentially in one of two electron bands produces the changes in the superconducting condensate, and ultimately destroys the superconductivity. Theoretical calculations predicted the charge-density wave transition.