Superconducting and Normal State Properties of OsB$_2$*

OsB$_{2}$ is a layered superhard metallic material that was found to superconduct below $T_{\rm c} = 2.1$~K.$^1$ We report the first detailed measurements of the static and dynamic magnetic susceptibilities $\chi$, electrical resistivity, heat capacity $C_{\rm p}$, penetration depth, and $^{11}$B NMR on OsB$_{2}$ to characterize its superconducting and normal state properties. The results confirm that OsB$_{2}$ is a bulk superconductor below $T_{\rm c} = 2.1$~K\@. Its properties can be described by a close to weak-coupling \emph{s}-wave BCS model with an electron-phonon coupling constant $\lambda = 0.4$--0.5, $\Delta(0)/(k_{\rm B}T_{\rm c}) \approx 1.9$, a small Ginzburg-Landau parameter $\kappa$ of order 5 or less, and a small zero-temperature critical magnetic field of roughly $500~$Oe. The $^{11}$B NMR measurements in the normal state show a nuclear spin-lattice relaxation time $T_1 = 2.1$~s at room temperature and a Korringa law with $T_1T = 610$~s$\cdot$K at lower $T$, and a correspondingly small $T$-independent Knight shift. These results indicate a small \emph{s} character of the conduction electron wave function at the B site at the Fermi level. Our results will be compared to corresponding data for MgB$_2$.\\ 1. J. K. Vandenberg et al., Mater. Res. Bull. {\bf 10}, 889 (1975).\\ $^*$Supported by the USDOE under Contract No.\ W-7405-Eng-82.\\ $\dagger$ Permanent address: Dept. Phys., The Catholic Univ. Korea.