Mass enhancement, correlations, and strong-coupling superconductivity in theβ-pyrochloreKOs2O6

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