Possible Anisotropic Order Parameter in Pyrochlore Superconductor KOs${}_2$O${}_6$ Probed by Muon Spin Rotation

Abstract

Magnetic penetration depth ($\lambda$) in a pyrochlore superconductor KOs${}_2$O${}_6$ was studied by means of muon spin rotation (\msr). The temperature dependence of transverse spin relaxation rate, which is proportional to ${\lambda }^{-2}$, exhibits a considerable deviation from that expected for the empirical two-fluid model ($\propto T^4$), rather obeying a $T^2$-tendency. Furthermore, $\lambda$ apparently increases with increasing applied field, suggesting the presence of nonlinear and nonlocal effects. These findings strongly suggest that the superconducting order parameter in KOs${}_2$O${}_6$ is anisotropic.

5 pages, 3 figures, submitted to J. Phys.: Cond. Matt