Magnetic Field Penetration Depth in the Heavy-Electron Superconductor UBe13

Abstract

We report the observation of a $T^2$ temperature dependence of the magnetic field penetration depth in U${\mathrm{Be}}_{13}$ at low temperatures. We show that this behavior is consistent with an anisotropic gap function for an axial $P$-wave state. Our results further show that the Landau parameter $F_{\mathrm{l}}^s$ appears to be small.