Superconductivity in FeSe: the role of nematic order

Abstract

Bulk FeSe is a special iron-based material in which superconductivity emerges inside a well-developed nematic phase. We present a microscopic model for this nematic superconducting state, which takes into account the mixing between $s-$wave and $d-$wave pairing channels and the changes in the orbital spectral weight promoted by the sign-changing nematic order parameter. We show that nematicity gives rise to a $\cos 2\theta$ variation of the pairing gap on the hole pocket that agrees with ARPES and STM data for experimentally-extracted Fermi surface parameters. We further argue that, in BCS theory, $d_{xz}$ and $d_{yz}$ orbitals give nearly equal contributions to the pairing glue, i.e. nematic order alone accounts for the gap anisotropy, but has little effect on $T_c$. This result questions the validity of the concept of orbital-selective pairing. Self-energy corrections, however, make $d_{xz}$ orbital more incoherent and reduce its contribution to pairing.

5pp, 3 figs, plus supplementary material, replaced with a published version

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• Nodal gaps in the nematic superconductor FeSe from heat capacity
• Revealing the single electron pocket of FeSe in a single orthorhombic domain
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• Raman response in the nematic phase of FeSe
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• Evidence for an Additional Symmetry Breaking from Direct Observation of Band Splitting in the Nematic State of FeSe Superconductor
• Preliminary Tc calculations for iron-based superconductivity in NaFeAs, LiFeAs, FeSe and nanostructured FeSe/SrTiO3 Superconductors
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• Revisiting the phase diagram of LaFe${}_{1-x}$Co${}_x$AsO on single crystals by thermodynamic methods
• Effect of the additional Se layer on the electronic structure of iron-based superconductor FeSe/SrTiO${}_3$
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