Displacement and annihilation of Dirac gap-nodes in d-wave iron-based superconductors

Abstract

Several experimental and theoretical arguments have been made in favor of a $d-$wave symmetry for the superconducting state in some Fe-based materials. It is a common belief that a $d-$wave gap in the Fe-based superconductors must have nodes on the Fermi surfaces centered at the $\Gamma$ point of the Brillouin zone. Here we show that, while this is the case for a single Fermi surface made out of a single orbital, the situation is more complex if there is an even number of Fermi surfaces made out of different orbitals. In particular, we show that for the two $\Gamma$-centered hole Fermi surfaces made out of $d_{xz}$ and $d_{yz}$ orbitals, the nodal points still exist near $T_c$ along the symmetry-imposed directions, but are are displaced to momenta between the two Fermi surfaces. If the two hole pockets are close enough, pairs of nodal points can merge and annihilate at some $T<T_c$, making the $d-$wave state completely nodeless. These results imply that photoemission evidence for a nodeless gap on the $d_{xz}/d_{yz}$ Fermi surfaces of KFe${}_2$As${}_2$ does not rule out $d-$wave gap symmetry in this material, while a nodeless gap observed on the $d_{xy}$ pocket in K${}_x$Fe${}_{2-y}$Se${}_2$ is truly inconsistent with the $d-$wave gap symmetry.

arXiv comment7 pages, 4 figures, submitted to PRB, references added

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• Weak-Pairing Higher Order Topological Superconductors
• Topological transition from nodal to nodeless Zeeman splitting in altermagnets
• Bogoliubov Fermi surfaces: General theory, magnetic order, and topology
• Hund interaction, spin-orbit coupling and the mechanism of superconductivity in strongly hole-doped iron pnictides
• Resilient nodeless $d$-wave superconductivity in monolayer FeSe
• Experimental consequences of Bogoliubov Fermi surfaces
• Nematic superconductivity in magic-angle twisted bilayer graphene from atomistic modeling
• Multiorbital singlet pairing and $d+d$ superconductivity
• Classification of Symmetry Derived Pairing at M Point in FeSe
• Superconductivity of anomalous pseudospin
• The Coulomb problem in iron based superconductors
• Nodal topology in $d$-wave superconducting monolayer FeSe
• Stability of Bogoliubov Fermi Surfaces within BCS Theory
• Spin-orbit-coupled superconductivity with spin-singlet non-unitary pairing
• Winding numbers of nodal points in Fe-based superconductors
• Detecting the topological winding of superconducting nodes via Local Density of States