  The phenomenology of the iron pnictide superconductor can be described by the
threeband s+- Eliashberg theory in which the mechanism of superconducting
coupling is mediated by antiferromagnetic spin fluctuations and whose
characteristic energy W0 scales with Tc according to the empirical law W0 =
4.65kBTc. This model presents the universal characteristics that are
independent of the critical temperature, such as the link between the two free
parameters l13 and l23 and the ratio Di/kBTc.
