Universal Amax/Tc in Fe-based superconductors

Iron-based superconductors display a large degree of variability in electronic structure at the Fermi surface, resulting in superconducting gap structures, Tc's, and other properties that vary considerably from family to family. Recently, it was noted that across many different families of Fe-based systems, the ratio Amax/Tc is found to be quasiuniversal with a large value of similar to 3.5 compared to the one-band BCS weak-coupling result of 1.76. Here, Amaxis the measured maximum gap across the Fermi surface. This remarkable fact was attributed to strong-coupling effects arising from Hund's metal physics. Here, we perform a "high-throughput" scan across band masses, Fermi energies, and interaction parameters in a weak-coupling Suhl-Matthias-Walker model. We find that unexpectedly large values of Amax/Tc can be achieved within weak coupling, and that quasiuniversal behavior similar to experiment emerges for those systems where interband interactions dominate intraband ones. However, within the current framework, a large mass contrast between bands is required.