Strong electron-phonon coupling in the intermetallic superconductor Mo8Ga41

Crystals of superconducting Mo8Ga41 (T-c = 9.8K) and Mo8-xVxGa41 limited solid solution [x(max) = 1.9(2)] have been grown from the high-temperature Ga flux and confirmed to have the V8Ga41 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 Mo8Ga41. The discontinuity in the heat capacity at T-c, Delta c(p)/gamma NTc = 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(ep) = 0.9. The upper critical field is mu H-0(c2)(0) = 8.3 T, while the lower one is only mu H-0(c1)(0) = 131 Oe. The upper critical field of Mo8Ga41 exhibits a clear enhancement with respect to the Werthamer-Helfand-Honenberg prediction, consistent with the strong electron-phonon coupling. The Mo8-xVxGa41 limited solid solution also exhibits superconducting properties, and the critical temperature T-c is reduced only slightly with increasing x.