Comparative optical reflectance study of the superconducting KHg-graphite and CsBix-graphite intercalation compounds

Abstract

We report the results of a comparative optical reflectance study at room temperature of the stage-1 and stage-2 CsBix and KHg graphite intercalation compounds (GIC’s) in the energy range 0.2–10 eV. A Kramers-Kronig analysis is carried out to determine the dielectric function ε(ω)=ε1(ω)+ε2(ω) and the intra- and interband contributions to ε(ω) are identified. The dielectric function for the respective compounds are analyzed in terms of a schematic density-of-states model involving contributions from two-dimensional graphite π band(s) and intercalate bands. Separate contributions from the π and intercalate electrons to the free-carrier plasma frequency are determined via the identification of the carbon π→π* interband absorption threshold ET∼2EF, where EF is the Fermi energy measured with respect to the approximate mirror plane in the carbon π-band structure. The analysis of the optical data indicates that for CsBix GIC’s, the electrical transport properties should be dominated by the light carbon π-band electrons in contrast to the KHg GIC’s, where the analysis indicates the transport properties should strongly depend on free carriers in both the π* and the intercalate band(s). In the case of KHg GIC’s, our interpretation of the experimental results are consistent with significant occupation of electronic states with Hg(6s) character. Our results suggest that nature of the superconductivity in the KHg and CsBix GIC’s should be quite different.

Source-reported materials — not catalogue approval

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