C-axis nodal lines induced by interlayer pairing in iron-based superconductors

Abstract

A layered superconductor with a full pairing energy gap can be driven into a nodal superconducting (SC) state by interlayer pairing when the SC state becomes more quasi-three-dimensional. We propose that this mechanism is responsible for the observed nodal behavior in a class of iron-based SCs. We show that the intra- and interlayer pairings generally compete and the gap nodes develop on one of the hole Fermi surface pockets as they become larger in the iron pnictides. Our results provide a natural explanation of the $c$-axis gap modulations and gap nodes observed by angle-resolved photoemission spectroscopy. Moreover, we predict that an anticorrelated $c$-axis gap modulation on the hole and electron pockets should be observable in the ${S}^{\ifmmode\pm\else\textpm\fi{}}$-wave pairing state.