Pair density modulation is a phenomenon recently observed in exfoliated flakes of iron-based superconductors, in which the superconducting gap oscillates strongly with the same periodicity as the underlying crystalline lattice. We propose a model that explains this modulation in systems with broken intra-unit-cell symmetries through the emergence of nematic superconductivity, which further breaks the four-fold rotation symmetry. This results in a sublattice texture on the Fermi surface, aligned with the anisotropic superconducting gap of the nematic s± + d state. This gives rise to distinctive gap maxima and minima located on the two inequivalent iron sublattices while still being a zero-momentum pairing state. We discuss how further investigation of such modulations can give insight into the nature of the superconducting pairing, such as the signs of the order parameters and visualization of a phase transition to a mixed two-component state using local probes. The authors present a theoretical mechanism for the recently-observed pair density modulation in exfoliated flakes of the iron-based superconductor FeTe0.55Se0.45. The mechanism is based on the appearance of a nematic mixed s± + d superconducting phase in a system with broken glide mirror symmetry.
Papaj et al. (Fri,) studied this question.