An investigation of the interrelationship between pressure and correlation in LaFeAsO under pressure

Highlights: • We investigated the interrelationship between pressure and correlation in the LaFeAsO. • The calculations were done by DFT + DMFT method. • The orbital switching induces a switching behavior between high and low TC. • Our calculations show the significant role of the orbital degrees of freedom in FeSCs. • We found the crucial role of the xy orbital in superconductivity in these materials. - Abstract: Here, we investigated the interrelationship between pressure and correlation in the LaFeAsO compound by the density functional theory method combined with the dynamical mean field theory (DFT + DMFT) method. The spectral function and the occupation number (ON) of Fe-3d orbitals at different pressures were extracted from the calculations, and the importance of the role of correlation in superconductivity in iron-based compounds was indicated. The measured ON of Fe-3d orbitals demonstrated charge transfer between them and also the crucial role of the Fe-3d_xy (xy) orbital in superconductivity in these materials. A switching behavior between high and low T_C through decreasing the correlation was observed in our calculations, originating from the orbital switching. This shows the significant role of the orbital degrees of freedom in iron-based superconductors.