Effect of rattling Phonons on Superconductivity of KOs_2O_6

Abstract

We model the electron coupling to anharmonic (rattling) mode in β-pyrochlore superconductor KOs2O6 by a sharply peaked electron-phonon coupling function α2F(Ω) centered at the mode energy. The strong-coupling Eliashberg equations are solved for the transition temperature Tc and the gap function ∆(ω,T) for a series of temperatures 0 < T < Tc. From these solutions, we obtain the temperature dependence of the gap edge ∆(T), the nuclear magnetic resonance (NMR) relaxation rate and the microwave conductivity for several values of the electron-phonon coupling parameter λ. The results are compared with the available experimental results 0 for KOs2O6