Anomalous scaling of ΔC versus Tc in the Fe-based superconductors: the -wave pairing state model

Abstract

The strong power law behavior of the specific heat jump ${\rm{\Delta }}C\;$ versus T _c $({\rm{\Delta }}C/{T}_{{\rm{c}}}\sim {T}_{{\rm{c}}}^{\alpha },\alpha \approx 2)$ , first observed by Bud’ko et al (2009 Phys. Rev. B http://dx.doi.org/10.1103/PhysRevB.79.220516 79 http://dx.doi.org/10.1103/PhysRevB.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 ${\rm{\Delta }}C\;$ versus T _c is a generic property of the multiband superconducting state paired by a dominant interband interaction ( ${V}_{\mathrm{inter}}\gt {V}_{\mathrm{intra}}$ ) reflecting the relation $\frac{{{\rm{\Delta }}}_{{\rm{h}}}}{{{\rm{\Delta }}}_{{\rm{e}}}}\sim \sqrt{\frac{{N}_{{\rm{e}}}}{{N}_{{\rm{h}}}}}$ near T _c , as in the ${S}_{\pm }$ -wave pairing state. We also found that this ${\rm{\Delta }}C\;$ 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 ${{\rm{\Gamma }}}_{0}$ (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.

Keywords

• Fe-based superconductors
• specific heat jump versus Tc
• BNC scailing
• S±-pairing state
• two band model
• 74.20.-z