Half-skyrmion picture of single hole doped CuO_2 plane
  Based on the Zhang-Rice singlet picture, it is argued that the half-skyrmion is created by the doped hole in the single hole doped high-T_c cuprates with N'eel ordering. The spin configuration around the Zhang-Rice singlet, which has the form of superposition of the two different d-orbital hole spin states, is studied within the non-linear \sigma model and the CP^1 model. The spin configurations associated with each hole spin state are obtained, and we find that the superposition of these spin configuration turns out to be the half-skyrmion that is characterized by a half of the topological charge. The excitation spectrum of the half-skyrmion is obtained by making use of Lorentz invariance of the effective theory and is qualitatively in good agreement with angle resolved photoemission spectroscopy on the parent compunds. Estimated values of the parameters contained in the excitation spectrum are in good agreement with experimentally obtained values. The half-skyrmion theory suggests a picture for the difference between the hole doped compounds and the electron doped compounds. 
T. Morinari