Strong electron-phonon coupling and multiband effects in the superconducting β-phase Mo1-xRex alloys

Superconducting transition temperature TC of some of the cubic beta phase Mo1-xRex alloys with x > 0.10 is an order of magnitude higher than that in the elements Mo and Re. We investigate this rather enigmatic issue of the enhanced superconductivity with the help of experimental studies of the temperature dependent electrical resistivity (rho(T)) and heat capacity (C-P(T)), as well as the theoretical estimation of electronic density of states (DOS) using band structure calculations. The rho(T) in the normal state of the Mo1-xRex alloys with x >= 0.15 is distinctly different from that of Mo and the alloys with x < 0.10. We have also observed that the Sommerfeld coefficient of electronic heat capacity gamma, superconducting transition temperature T-C and the DOS at the Fermi level show an abrupt change above x > 0.10. The analysis of these results indicates that the value of electron-phonon coupling constant lambda(ep) required to explain the T-C of the alloys with x > 0.10 is much higher than that estimated from gamma. On the other hand the analysis of the results of the rho(T) reveals the presence of phonon assisted inter-band s-d scattering in this composition range. We argue that a strong electron-phonon coupling arising due to the multiband effects is responsible for the enhanced TC in the beta phase Mo1-xRex alloys with x > 0.10.