Pair density modulation from rotational and glide symmetry breaking

Spatially modulated superconducting order parameters are usually associated with breaking of the space-group symmetries of the crystal. However, recently it has been demonstrated that strong gap modulation on the length scale of the unit cell, called pair density modulation (PDM) state, can be present in thin flakes of FeTeSe superconductor. In this talk I will demonstrate how the breaking of glide mirror symmetry, combined with nematicity in the next-nearest-neighbor iron direction can result in this large gap modulation. Breaking of both of these intra-unit-cell symmetries is crucial for the appearance of PDM. Broken glide mirror symmetry results in a sublattice texture on the Fermi surface, and nematicity causes the unequal split of the Fermi surface between the two iron sublattices. This mechanism suggests that PDM can be induced in other iron superconductors, for example by strain application, and its further study could provide valuable insight about the nature of the superconducting order in iron compounds.