Quasiparticle scattering interference in (K,Tl)FexSe2 superconductors

Abstract

We model the quasiparticle interference (QPI) pattern in the recently discovered (K,Tl)FexSe2 superconductors. We show in the superconducting state that, due to the absence of hole pockets at the Brillouin zone center, the quasiparticle scattering occurs around the momentum transfer q = (0,0) and (±π,±π) between electron pockets located at the zone boundary. More importantly, although both dx2−y2-wave and s-wave pairing symmetry lead to nodeless quasiparticle excitations, distinct QPI features are predicted between both types of pairing symmetry. The so-called Z-map of the QPI exhibits strongest scattering with q = (±π,±π) for the dx2−y2-wave pairing symmetry, which is absent in the case of an isotropic s-wave pairing symmetry. The significant contrast in the QPI pattern between the dx2−y2-wave and the isotropic s-wave pairing symmetry can be used to probe the pairing symmetry within the Fourier-transform STM technique.