Fermi surface in the superconductingβ-pyrochlore oxideCsOs2O6

Abstract

We report de Haas--van Alphen effect (dHvA) measurements and band-structure calculations for $\mathrm{Cs}{\mathrm{Os}}_{2}{\mathrm{O}}_{6}$. Sixteen dHvA frequency branches are observed in the $(\overline{1}10)$ plane. The Fermi surface consists of hole and electron surfaces. The topology of the measured Fermi surface can be described by the band-structure calculations if slight rigid band shifts are incorporated. The electron surface has through holes in the ⟨111⟩ directions, indicating that the van Hove singularity is above the Fermi level unlike previously thought. Using band-structure results, we have estimated that the Stoner enhancement factor $S\ensuremath{\sim}3.1$ and that the Wilson ratio $R\ensuremath{\sim}0.86$. The dHvA effective masses are mostly between three and four times the corresponding band masses, which is consistent with the specific-heat mass enhancement of 3.6. We have also estimated the orbital-specific Stoner enhancement factor for one orbit from dHvA data: the most probable value of the product $Sg$, where $g$ is the $g$ factor, for that orbit is found to be 9.374. The small Wilson ratio and Stoner enhancement indicate rather limited importance of electron-electron interactions in $\mathrm{Cs}{\mathrm{Os}}_{2}{\mathrm{O}}_{6}$.