Routes to probe Bismuth induced strong-coupling superconductivity in bimetallic BiIn alloys.

We report the observation of strong electron-phonon coupling in intergranular linked BiIn superconductors over an infinite range mediated by low-lying phonons. An enhanced superconducting transition temperature was observed from the magnetization, revealing a main diamagnetic Meissner state below TC(0) = 5.86(1) K and a critical field HC(0) = 1355(15) Oe with an In2Bi phase of the composite sample. The electron-phonon coupling to low lying phonons is found to be the leading mechanism for observed strong-coupling superconductivity in the BiIn system. Our findings suggest that In2Bi is in the strong-coupling region with TC(0) = 5.62(1) K, λep = 1.45, ωln = 45.92 K and α = 2.23. The estimated upper critical field can be well-described by a power law with α value higher than 2, consistent with the strong electron-phonon coupling.