Different roles of Zn$^{2+}$ and Li$^{+}$ impurities in the CuO$_2$ plane in undoped cuprate compounds

Abstract

A planar Mott insulator with easy plane N\'eel order can be mapped onto a Gutzwiller-projected spin Hall state. The in-plane substitution of Zn$^{2+}$ and Li$^{+}$ for Cu$^{2+}$ brings zero modes around the spin vacancy. The Gutzwiller projection precludes single particle excitations, however, preserves the zero modes which have a local spin moment for Zn$^{2+}$ and a local charged hole for Li$^{+}$, respectively. While the local spin moment for Zn$^{2+}$ is screened by the long-range spin correlations, the active charge degree of freedom for Li$^{+}$ impurity twists the spin background with long ranged disturbances. This proposal explains the very different roles of the Zn$^{2+}$ and Li$^{+}$ impurities on the magnetic perturbations in the CuO$_2$ plane in the undoped cuprate compounds.