Prediction of the in-Gap States Above the Top of the Valence Band in the Undoped Insulating Cuprates due to Spin-Polaron Effect

In the framework of the generalized tight binding method we have calculated the quasiparticle band structure and the spectral functions of the undoped cuprates like $La_2 CuO_4$, $Sr_2CuO_2Cl_2$ etc. Due to spin fluctuations the in-gap state appears above the top of the valence band in the undoped antiferromagnetic insulator similar to in-gap states induced by hole doping. In the ARPES experiments the in-gap states can be detected as weak low energy satellites.