Mass enhancement, correlations, and strong coupling superconductivity in the beta-pyrochlore KOs2O6

Abstract

To assess electron correlation and electron-phonon coupling in the recently discovered beta-pyrochlores KOs2O6 and RbOs2O6, we have performed specific heat measurements in magnetic fields up to 14 T. We present data from high quality single crystalline KOs2O6, showing that KOs2O6 is a strong coupling superconductor with a coupling parameter lambda_ep \approx 1.0 to 1.6 (RbOs2O6: lambda_ep \approx 1). The estimated Sommerfeld coefficient of KOs2O6, gamma=76 to 110 mJ/(mol K^2), is twice that of RbOs2O6 [gamma=44 mJ/(mol K^2)]. Using strong-coupling corrections, we extract useful thermodynamic parameters of KOs2O6. Quantifying lambda_ep allows us to determine the mass enhancement over the calculated band electronic density of states. A significant contribution in addition to the electron-phonon term of lambda_c=1.7 to 4.3 is deduced. In an effort to understand the origin of the enhancement mechanism, we also investigate an unusual energetically low-lying phonon. There are three phonon modes per RbOs2O6, suggestive of the phonon source being the rattling motion of the alkali ion. This dynamic instability of the alkali ions causes large scattering of the charge carriers which shows up in an unusual temperature dependence of the electrical resistivity.

Accepted for publication in PRB

References in corpus (17)

• Superconductivity at 1 K in Cd2Re2O7
• New Pyrochlore Oxide Superconductor RbOs2O6
• Superconductivity in the Correlated Pyrochlore Cd_2Re_2O_7
• New beta-Pyrochlore Oxide Superconductor CsOs2O6
• Correlation Effects and Structural Dynamics in the $\beta$-Pyrochlore Superconductor KOs${}_2$O${}_6$
• Electronic structure of the pyrochlore metals Cd2Os2O7 and Cd2Re2O7
• Magnets with strong geometric frustration
• Superconductivity in Geometrically Frustrated Pyrochlore RbOs2O6
• Effects of Crystal Structure and the On-Site Coulomb Interactions on the Electronic and Magnetic Structure of Pyrochlores $A_2$Mo${}_2$O${}_7$ (A= Y, Gd, and Nd)
• Second Anomaly in the Specific Heat of beta-Pyrochlore Oxide Superconductor KOs2O6
• Specific Heat of the beta-Pyrochlore Oxide Superconductors CsOs2O6 and RbOs2O6
• Pressure effects on the transition temperature and the magnetic field penetration depth in the pyrochlore superconductor RbOs_2O_6
• Possible Anisotropic Order Parameter in Pyrochlore Superconductor KOs${}_2$O${}_6$ Probed by Muon Spin Rotation
• Electronic structure properties and BCS superconductivity in beta-pyrochlore oxides: KOs_2O_6
• Evidence for s-wave superconductivity in the new beta-pyrochlore oxide RbOs2O6
• Erratum to Three Papers on the beta-Pyrochlore Oxide Superconductors
• Intrinsic thermodynamic properties of the pyrochlore superconductor RbOs2O6 extracted by condensation energy analysis

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