Enhanced Superconductivity by Electron Renormalization of a Directly Observed Brout-Visscher Local Phonon: Re inMo1xRex

Abstract
Tunneling reveals a ∼14-meV resonance mode of Re in Mo1xRex, 0.2<x<0.4, which contributes strongly to α2F(ω) and to strong coupling, 2ΔkTc3.53=δ>0. The anomalous softening and width of the resonance mode are consistent with the standard theory of phonon renormalization by the electron gas. These unexpected results explain the low-N(0), high-Tc behavior of Mo0.6 Re0.4 and possible Nb3Ge.