Strong electron-phonon coupling in the intermetallic superconductor Mo₈Ga₄₁

Crystals of superconducting Mo$_{8}$Ga$_{41}$ ($T_{\text{c}}=9.8$ K) and Mo$_{\text{8-x}}$V$_{\text{x}}$Ga$_{41}$ limited solid solution $(x_{\text{max}}=1.9(2))$ have been grown from the high-temperature Ga flux and confirmed to have the V$_{8}$Ga$_{41}$ type of crystal structure at room temperature. Thermodynamic and transport measurements as well as electronic structure calculations were performed to investigate both normal- and superconducting-state properties of Mo$_{8}$Ga$_{41}$. The discontinuity in the heat capacity at $T_{\text{c}}$, $\Delta{}c_{\text{p}}/\gamma_{\text{N}}T_{\text{c}}=2.83$ in zero magnetic field, indicates a much stronger electron-phonon coupling than in the standard BCS limit. From the heat capacity data, we estimated the electron-phonon coupling constant $\lambda_{\text{ep}}=0.9$. The upper critical field is $\mu_{0}H_{\text{c2}}(0)=8.3$ T, while the lower one is only $\mu_{0}H_{\text{c1}}(0)=131$ Oe. The upper critical field of Mo$_{8}$Ga$_{41}$ exhibits a clear enhancement with respect to the Werthamer-Helfand-Honenberg prediction, consistent with the strong electron-phonon coupling. The Mo$_{\text{8-x}}$V$_{\text{x}}$Ga$_{41}$ limited solid solution also exhibits superconducting properties, and the critical temperature $T_{\text{c}}$ is reduced only slightly with increasing $x$.