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 $L{a}_{2}Cu{O}_4$, $S{r}_{2}Cu{O}_{2}C{l}_2$ 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.