Nodeless Superconductivity in the Noncentrosymmetric Superconductor $M{g}_{10}I{r}_{19}{B}_{16}$

We measured the resistivity, diamagnetization and low temperature specific heat of the newly discovered noncentrosymmetric superconductor $M{g}_{10}I{r}_{19}{B}_{16}$. It is found that the superconducting gap has an s-wave symmetry with a value of about ${\mathrm{\Delta }}_0\approx$ 0.6 meV, and the ratio ${\mathrm{\Delta }}_0\mathrm{/}{k}_B{T}_c\approx 1.86$ indicates a weak coupling for the superconductivity. The correlations among the normal state Sommerfeld constant ${\gamma }_n$, the slope $-d{\mu }_0{H}_{c2}(T)\mathrm{/}dT$ near Tc and the condensation energy Ec are all consistent with the weak coupling picture. The separated phonon contribution from the specific heat shows that the conduction electrons of the $Ir$ atoms interact most strongly with the vibrations of themselves, instead of with that of the light element boron.