Impurity effects on quasiparticle dispersion in a d-wave superconductor

The effects of nonmagnetic impurity on the renormalization of quasiparticle (QP) dispersion in a d_x²−y²-wave superconductor are investigated theoretically using the self-consistent t-matrix approximation. It is shown that the kink in the dispersion around the antinodal region is weakened and disappears eventually with the increase in impurity concentration. In the meantime, the dip in the peak/dip/hump structure of the QP line shape is smeared out and the peak is suppressed and broadened upon the introduction of impurities. We attribute these effects to the suppression and broadening of the spin-resonance mode by impurity, which is coupled strongly to quasiparticles. These results are consistent qualitatively with the recent experiments and give support to the scenario that the quasiparticle renormalization around the antinodal region is mainly of magnetic origin.