Anomalous temperature dependence of spin susceptibility around a nonmagnetic impurity in high-T_c cuprate superconductors

Local magnetic properties around a nonmagnetic impurity are investigated in the superconducting state of high-T_c cuprates. We consider a model two-dimensional d_x2-y2-wave superconductor with strong antiferromagnetic (AF) spin fluctuations and calculate the spin susceptibility around the impurity. We show that the uniform susceptibility, which is usually suppressed in spin-singlet superconductivity, increases with decreasing temperature around the impurity when the impurity scattering is in the unitarity limit. This anomalous temperature dependence is more remarkable when the impurity potential is extended spatially and the AF spin fluctuations are stronger. Our results agree with the anomalous temperature dependence of the Knight shift on Li that was recently observed in YBa₂(Cu_1-xLi_x)₃O_6+y.