On the other hand RbBi2 and CsBi2 are in contrast with CaBi2, which crystallizes in an orthorhombic structure that can be viewed in a distorted Laves phase structure, in which tetrahedrons are distorted to Bi-Bi and Ca-Bi planes separated from each other. Here the phonon linewidths are smaller and average Bi frequencies are higher, leading to the EPC constant λep = 0.54, much lower than λep = 0.82 and λep = 0.87 for RbBi2 and CsBi2, respectively, despite the value of I = 1.17 lying between RbBi2 and CsBi2 cases. This results in a lower critical temperature (Tc = 2.0 K for CaBi2) . It is worth mentioning that the average Bi frequency in elemental Bi, the phonon structure of which is presented in Fig. of the Supplementary Material and summarized in Table , is also higher than in the studied Laves phases. Since Bi is a semimetal, the DOS(EF) and the value of I are small, leading to a low value of the EPC parameter λep = 0.23 and very low predicted critical temperature Tc = 0.7 mK in a fair agreement with the experimental Tc = 5 mK .