Magnetic penetration depth inRbOs2O6studied by muon spin rotation

Abstract

Measurements of the magnetic field penetration depth $\ensuremath{\lambda}$ in the pyrochlore superconductor ${\mathrm{RbOs}}_{2}{\mathrm{O}}_{6}$$({T}_{c}\ensuremath{\simeq}6.3\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ were carried out by means of the muon-spin-rotation $(\ensuremath{\mu}\mathrm{SR})$ technique. At low temperatures ${\ensuremath{\lambda}}^{\ensuremath{-}2}(T)$ saturates and becomes constant below $T\ensuremath{\simeq}0.2{T}_{c}$, in agreement with what is expected for weak-coupled $s$-wave BCS superconductors. The value of $\ensuremath{\lambda}$ at $T=0$ was found to be in the range of 250--300 nm. $\ensuremath{\mu}\mathrm{SR}$ and equilibrium magnetization measurements both reveal that at low temperatures $\ensuremath{\lambda}$ is almost (at the level of 10%) independent of the applied magnetic field. This result suggests that the superconducting energy gap in ${\mathrm{RbOs}}_{2}{\mathrm{O}}_{6}$ is isotropic.