Mathematical and Physical Properties of Three-Band s+- Eliashberg Theory for Iron Pnictides

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.