this method has the uncertainty of small leakage of other orbitals into the chosen regions, which is the cause of the finite residual value for the [$d_{xy}$]{} curve, the contrasting behavior of the [$d_{xy}$]{} versus [$d_{xz}$/$d_{yz}$]{} orbitals is clearly demonstrated. A temperature cycle test was performed to exclude the possibility of sample aging (see SI). Measurements on the sister compound RFS reveal similar behavior (SI), suggesting the generality in this family of superconductors. This observation of a selected orbital that loses coherent spectral weight while the others remain metallic is reminiscent of a crossover into an OSMP in which selected orbitals become Mott localized while others remain metallic.

![image](Fig4new){width="95.00000%"}

To further understand this phenomenon, we perform theoretical calculations based on a five-orbital Hubbard model to study the metal-to-insulator transition (MIT) in the paramagnetic phase using a slave-spin mean-field method [@30yu; @31demedici05]. At commensurate electron filling n=6 per Fe (corresponding to Fe2$^+$ of the parent FeSC), we find the ground state of the system to be a metal, an OSMP or a MI depending on the intra-orbital repulsion U and the Hund’s coupling J. Furthermore, the MIT can be triggered by increasing temperature (Fig. \[fig:fig4\](a)) due to the larger entropy of 