We measured the resistivity, diamagnetization, and low-temperature specific heat of the newly discovered noncentrosymmetric superconductor ${\mathrm{Mg}}_{12-\delta }{\mathrm{Ir}}_{19}{\mathrm{B}}_{16}$. The temperature dependence of specific heat is consistent with the model of an isotropic $s$-wave gap with value ${\Delta }_0\approx 0.94\mathrm{meV}$ for the sample $T_c=5.7\mathrm{K}$, and the ratio ${\Delta }_0∕k_B{T}_c\approx 1.91$ indicates a slightly moderate coupling for the superconductivity. The correlations among the normal state Sommerfeld constant ${\gamma }_n$, the slope $-d{\mu }_0{H}_{c2}\left(T\right)∕dT$ near $T_c$, and the condensation energy $E_c$ are all consistent with the slightly moderate coupling picture. Based on the data of phonon contribution, $T_c$ and the McMillan formula, we obtained an electron-phonon coupling strength ${\lambda }_{e\text{−}\mathrm{ph}}\approx 0.66$, which suggests that the superconductivity here is induced by the electron-phonon coupling.

• Received 25 May 2007

DOI:https://doi.org/10.1103/PhysRevB.76.064527