Conventional $s$-Wave Superconductivity in Noncentrosymmetric   Ir$_2$Ga$_9$: $^{71}$Ga-NQR Evidence
  We report a $^{71}$Ga nuclear-quadrupole-resonance (NQR) study on the characteristics of superconductivity in noncentrosymmetric Ir$_2$Ga$_9$ at zero field (H=0). The $^{71}$Ga-NQR measurements have revealed that $1/T_1$ has the clear coherence peak just below $T_{\rm c}$, and decreases exponentially upon further cooling in Ir$_2$Ga$_9$. From these results, Ir$_2$Ga$_9$ is concluded to be the conventional s-wave superconductor. Despite the lack of spatial centrosymmetry, there are no evidence for unconventional superconducting state ascribed to ASOC in Ir$_2$Ga$_9$. 
A. Harada, N. Tamura, H. Mukuda, Y. Kitaoka, K. Wakui, S. Akutagawa,   and J. Akimitsu