Broken symmetry of in-gap quasiparticle excitations in superconducting FeSe(001) with high defect density

FeSe(001) with a high defect density was studied in the superconductiong phase by means of scanning tunneling spectroscopy at low temperature. Quasiparticle excitations surrounding structural defects are found inside the superconducting gap. This spectral intensity is used for revealing additional scattering channels for the quasiparticle excitations. The related wave vectors are located around the $M$ points of the Brillouin zone and follow ${C}_{2}$ symmetry. We attribute the symmetry and the observed lack of dispersion of the scattering channels to the interaction of Bogoliubov quasiparticles with nematic order.