Half-skyrmion picture of single hole doped high-T_c cuprate
  The single hole doped CuO_2 plane is studied by the O(3) non-linear \sigma model and its CP^1 representation. It is argued that the spin configuration around a Zhang-Rice singlet is described by a half-skyrmion. The form of the excitation spectrum of the half-skyrmion is the same as that in the \pi-flux phase. 
Takao Morinari