Following recent theoretical and experimental investigations of superconductivity in the graphite intercalated compounds CaC6and SrC6, we report on a very low temperature magnetisation study on BaC6down to 80 mK. The data show no trace of superconductivity even at fields as low as 0.7 Oe. Using a McMillan parametrisation of the BCS parameters, we conclude that the Coulomb pseudopotential is expected to be as large as 0.19 in both BaC6and SrC6, i.e. 40% larger than in CaC6. As an alternative scenario, we argue that extrinsic effects such as intercalant disorder may depress superconductivity in both BaC6and SrC6, as in the case of CaC6. © 2007 Elsevier Ltd. All rights reserved.
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