Anomalous scaling of ΔC versus Tc in the Fe-based superconductors: the S+/-wave pairing state mode

Abstract

The strong power law behavior of the specific heat jump Delta C versus T-c(Delta C/T-c similar to T-c(alpha), alpha approximate to 2), first observed by Bud'ko et al (2009 Phys. Rev. B 79 220516), has been confirmed with several families of the Fe-based superconducting compounds with various dopings. We have tested a minimal two band BCS model to understand this anomalous behavior and showed that this non-BCS relation between Delta C versus Tc is a generic property of the multiband superconducting state paired by a dominant interband interaction (V-inter > V-intra) reflecting the relation Delta(h)/Delta(e) similar to root N-e/N-h near T-c, as in the S-+/--wave pairing state. We also found that this Delta C versus T-c power law can continuously change from the ideal BNC scaling to a considerable deviation by a moderate variation of the impurity scattering rate Gamma(0) (non-pair-breaking). As a result, our model provides a consistent explanation why the electron-doped Fe-based superconductors follow the ideal BNC scaling very well while the hole-doped systems often show varying degree of deviations.