${}^{17}\mathrm{O}$ NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high $T_C$ ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above $T_C$, with a typical extension $\xi =3$ cell units for Zn and $\xi \ge 3$ for Ni. In addition, Zn is observed to induce a local density of states near the Fermi energy in its neighborhood, which also decays over about 3 cell units. Its magnitude decreases sharply with increasing temperature. This allows direct comparison with the STM observations done in BiSCCO.

• Received 27 April 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.127005