Pressure effects on the electronic properties and superconductivity in the β-pyrochlore oxides: AOs₂O₆ (A = Na, K, Rb, Cs)

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We present a first-principles study of the electronic structure and superconducting parameters of the compounds AOs₂O₆ (A = Na, K, Rb, and Cs) and at ambient and applied hydrostatic pressure. We find that the sensitivity of the density of states at the Fermi energy, E F, and related electronic properties to the size of the alkali metal atom as well as to applied pressure is driven by a van Hove singularity with energy very close to E F. Further, a computation of the superconducting parameters of these materials allows us to show that the observed change of Tc, both upon substitution of the alkali metal and under applied hydrostatic pressure, can be well understood within a phonon-mediated pairing scenario. In this regard, we find that the correction to the effective electron mass due to spin fluctuations plays a significant role.