Anomalous Scaling Relations and Pairing Mechanism of the Fe-based Superconductors

Abstract

The anomalous scaling behavior of the specific heat jump ΔC vs. , first observed by Bud’ko et al[], has been confirmed with several families of the Fe-based superconducting compounds with various dopings. And more recently, Xing et al[] have reported that the condensation energy (CE) vs. Tc also follows an anomalous power law with about forty different samples of the Fe-based superconductors. These apparently non-BCS power law relations have strongly hinted at a non-BCS pairing mechanism of the Fe-based superconductors. We have studied a minimal two band BCS model to understand these anomalous scaling behaviors and showed that these non-BCS relations of as well as can be well reproduced by the simple two-band BCS model paired by a dominant interband repulsive interaction (Vinter > Vintra > 0). The origin of these anomalous scaling relations are the kinematic constraint of near Tc of the two band BCS model, as realized in the S±-wave pairing state. Our results imply that these seemingly non-BCS-like scaling behaviors, on the contrary to the common expectations, are in fact strong experimental evidences that the pairing mechanism of the Fe-based superconductors is genuinely a BCS mechanism, meaning that the Cooper pairs are formed by the itinerant carriers glued by a pairing interaction.