Effects of pd-hybridization in strongly correlated insulator FeSi

• Strongly correlated compound FeSi investigated in the pd-hybridization model.
• Transfer states between p- and d-bands induces spin fluctuations in the insulator phase.
• Increasing spin fluctuation amplitude leads to the disappearance of hybridization gap.
• Spin susceptibility induced by fluctuations with increasing temperature.
• The result of the calculation of the susceptibility agrees with experiment.

We study the hybridization effects in the system of the strongly correlated d-electrons and the nearly free p-electrons. It has been established that there is the hybridization of the spin states of electrons in addition to the hybridization of p- and d-states of different atoms. This leads to the formation of four energy bands – spin-symmetrized and spin-antisymmetrized of singlets of A- and B-states. It has been shown that the increase of the temperature leads to a change of the number of d-like states, gaps into hybridization spectra of spin-antisymmetrized and spin-symmetrized states, and to the shift of these spectra relative to each other. Numerical analysis performed on an example of strongly correlated semiconductor iron monosilicide. The semi-quantitative description of the electronic and magnetic properties of this compound has been obtained. In particular, we obtained the disappearance of the semiconducting gap at 90 K and the values of temperatures corresponding to the features of the temperature dependence of the magnetic susceptibility.