Impurity Effects in Cuprate Superconductors

Abstract

In order to extract the information on the symmetry of the Cooper pair in high-T_c superconductors, we study non-magnetic impurity effects on the density of states for several pairing states in 2-dim. square lattice. The assumed states are s-, extended s- and d-wave pairing ones. Only when we assume an anisotropic pairing state such as a d-wave pairing, we can explain the experimental results on nuclear spin relaxation rate observed in Zn-doped YBa₂Cu₃O_7−δ.