LAUSR

Recent observations of two nodeless gaps in superconducting CeCu2Si2 have raised intensive debates on its exact gap structure of either sign reversal (s+−) or sign preserving (s) pairing. Here we investigate the quasiparticle interference (QPI) using the realistic Fermi surface topology for both weak and strong interband impurity scatterings. Our calculations of the QPI and integrated antisymmetrized local density of states reveal qualitative distinctions between s+− and s pairing states, that include the intra-gap impurity resonance and significant energy-dependence difference between two gap energies. Our predictions provide a guide for the phase-sensitive QPI measurements to uncover decisively the true pairing symmetry in the heavy fermion superconductor CeCu2Si2.