Nodal topology in $d$-wave superconducting monolayer FeSe

Abstract

A nodeless $d$-wave state is likely in superconducting monolayer FeSe on SrTiO${}_3$. The lack of nodes is surprising but has been shown to be a natural consequence of the observed small interband spin-orbit coupling. Here we examine the evolution from a nodeless state to the nodal state as this spin-orbit coupling is increased from a topological perspective. We show that this evolution depends strongly on the orbital content of the superconducting degrees of freedom. In particular, there are two $d$-wave solutions, which we call orbitally trivial and orbitally nontrivial. In both cases, the nodes carry a $\pm 2$ topological winding number that originates from a chiral symmetry. However, the momentum space distribution of the positive and negative charges is different for the two cases, resulting in a different evolution of these nodes as they annihilate to form a nodeless superconductor. We further show that the orbitally trivial and orbitally nontrivial nodal states exhibit different Andreev flat band spectra at the edge.

arXiv comment11 pages, 6 figures

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• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Nematic superconductivity in magic-angle twisted bilayer graphene from atomistic modeling
• Evidence for d-wave superconductivity in single layer FeSe/SrTiO3 probed by quasiparticle scattering off step edges
• Topological Superconductivity Induced by Magnetic Texture Crystals
• Pairing symmetry and topological surface state in iron-chalcogenide superconductors
• Detecting the topological winding of superconducting nodes via Local Density of States