Gap symmetry, modulation, and nematicity in exfoliated iron superconductors

Recent experiments have demonstrated that exfoliation of iron-based superconductors can lead to exotic new phenomena absent in the bulk crystals, even if the exfoliated flakes are not atomically thin. One example of such novel behavior is the emergence of pair density modulation in exfoliated Fe(Se, Te), where the two inequivalent iron sublattices exhibit gaps different by up to 30%. In this talk I will discuss how gap symmetry, modulation, and nematicity in iron-based materials are affected by exfoliation. I will show that the combination of glide symmetry breaking and a superconducting gap anisotropic in momentum space can lead to a substantial gap modulation between the two iron sublattices. I will also explore how exfoliation-induced changes in nematicity can affect the leading gap symmetry, and how exfoliation can have an effect similar to chemical substitution without the downsides of introducing inhomogeneities into the material. These effects thus establish studies of exfoliated iron-based superconductor flakes as a new frontier for better understanding the mechanisms that govern their phase diagrams.