Type-I Superconductivity in Ytterbium Diantimonide

The layered antimonide compound YbSb$_2$ crystallizes with a ZrSi$_2$-type orthorhombic structure, different from other rare earth diantimonides. Unusual for a binary compound, Type-I superconductivity has been observed in YbSb$_2$. In this talk, we present the results from anisotropic magnetization, resistivity, heat capacity and magneto-optical Faraday effect measurements on YbSb$_2$ single crystals, showing a clear superconducting transition at $T_c$ = 1.25 K. The estimated electron-phonon coupling $\lambda$ = 0.51, together with the jump in electronic specific heat $\Delta C_{es}/\gamma T_{c}$ = 1.36, indicate the system to be a weak-coupling BCS superconductor. Magnetization, as well as heat capacity measured under field, clearly suggest a Type-I behavior, which is confirmed by the estimated Ginzburg-Landau parameter $\kappa$ = 0.13. According to the $H$-$T$ phase diagram, the critical field $H_c$ is around 60 Oe.