Evidence for two-band superconductivity and non-magnetic pair breaking in Na0.3CoO2 1.3H2O; effects of sample ageN. Oeschler1, R. A. Fisher1, N. E. Phillips1, J. E. Gordon2, M.-L. Foo3 and R. J. Cava3
1 Lawrence Berkeley National Laboratory and Department of Chemistry, University of California - Berkeley, CA 94720, USA
2 Physics Department, Amherst College - Amherst, MA 01002, USA
3 Department of Chemistry, Princeton University - Princeton, NJ 08544, USA
received 6 February 2008; accepted in final form 31 March 2008; published May 2008
published online 16 May 2008
The specific heat of Na0.3CoO2 1.3H2O gives evidence of two electron bands with comparable densities of states and different superconducting-state energy gaps. A non-magnetic pair-breaking action, which acts preferentially in the band with the smaller gap, progresses with sample age. The two bands and non-magnetic pair breaking have implications for possible pairing mechanisms; the effects of the pair breaking constitute the "sample dependence" of the properties of this material. In concert with structural changes reported by others, the specific heat suggests dual roles for O vacancies -tuning the carrier concentration to favor superconductivity, and pair breaking to destroy it.
74.25.Bt - Thermodynamic properties.
74.25.Jb - Electronic structure.
74.62.Dh - Effects of crystal defects, doping and substitution.
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