Constraints on the total coupling strength to bosons in iron based superconductors

Abstract

At present, there is still no consistent interpretation of the normal and superconducting properties of Fe-based superconductors (FeSCs). The strength of the el-el interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for an important high-energy mass renormalization phenomenologically,and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, all FeSCs with $T_{\mathrm{c}}<$ 40~K studied so far are found to belong to an {\it intermediate} coupling regime. This finding is in contrast to the strong coupling scenarios proposed in the early period of the FeSC history.We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe${}_2$As${}_2$ (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the $\epsilon$-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field. pointing to its dominant role in the superconductivity of these three compounds.

19 pages, 9 figures

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Cited by in corpus (6)

• Emerging superconductivity with broken time reversal symmetry inside a superconducting $s$-wave state
• The Role of Odd-Frequency Pairing in Multiband Superconductors
• Increasing stripe-type fluctuations in $A$Fe${}_2$As${}_2$ ($A$ = K, Rb, Cs) superconductors probed by ${}^{75}$As NMR spectroscopy
• Mass enhancements and band shifts in strongly hole overdoped Fe-based pnictide superconductors: KFe${}_2$As${}_2$ and CsFe${}_2$As${}_2$
• Temperature dependence of NMR Knight shift in pnictides: proximity to a van Hove singularity
• Enhanced critical temperatures in the strongly overdoped iron-based superconductors AFe${}_2$As${}_2$ (A = K, Cs, Rb) observed by point contacts