Evidence for s-wave superconductivity in the β-pyrochlore oxide RbOs2O6 -: art. no. 024524

We report the results of Rb-87 NMR measurements on RbOs2O6, a member of the family of the superconducting pyrochlore-type oxides with a critical temperature T-c=6.4 K. In the normal state, the nuclear spin-lattice relaxation time T-1 obeys the Korringa-type relation T1T=const and the Knight shift is independent of temperature, indicating the absence of strong magnetic correlations. In the superconducting state, T-1(-1)(T) exhibits a tiny coherence enhancement just below T-c, and decreases exponentially with further decreasing temperatures. The value of the corresponding energy gap is close to that predicted by the conventional weak-coupling BCS theory. Our results indicate that RbOs2O6 is a conventional s-wave-type superconductor.