Probing nonlinear structure-orbital correlation for PrOFe$_{0.9}$Co$_{0.1}$ as under pressure

Fe-based pnictides have evolved as a practical alternative to Cuprate superconductors. Electrons are transported along As–Fe–As path of inter-connected FeAs$_4$, utilizing Fe 3d-As 4p orbital hybridization. This leads to an obvious question — what are the key tetrahedral parameters that control hybridization? Unfortunately, empirical results from discrete experiments generated conflicting structure-transport correlations. The present work attempts to fill this logistic gap by probing the missing structure-orbital correlation link. To this effect, pressure-dependent XRD and As K-edge XANES were measured on the same sample set of PrOFe$_{0.9}$Co$_{0.1}$As. A point of inflection emerges at the compressibility limit of Fe–As bond-length. At this point, the trajectory of As atom and (correspondingly) parameters of FeAs4 undergo parabolic reversal whilepd hybridization undergoes nonreversible maximization. This incongruence generates nonlinear structure-orbital correlation, which is a novel finding. Two novel concepts emanate from this exercise — (a) compressibility limit of Fe–As bond-length emerges as the new critical reference and (b) nonlinearity warrants that pd hybridization is sensitive to the phase of As trajectory (relative to this reference) rather than the absolute values of tetrahedral parameters. ... mehrThese mark major corrections from previous works, which should settle the existing conflicts.