An infrared study of electron delocalization in Mn-based relatives of the pnictides

Current data suggest that the viability of parent compounds to become superconducting is intimately tied to electron correlations.\footnote{M. Quazilbash \textit{et. al.} Nature Physics 5, 647 (July 2009)}$^,$\footnote{P.A. Lee \textit{et. al.} Reviews of Modern Physics 78, 17 (January 2006)} Further comparisons between the ground states of the cuprate and pnictide parent compounds indicate that doping across an electron delocalization transition (EDT) may be key to obtaining a higher critical temperature.\footnote{J. Simonson \textit{et. al.} ArXiv:11105938} These insights lead us to study the Mn-based compounds that are isostructural with pnictides and are antiferromagnetic insulators like the cuprates. Specifically, we have explored the effects of doping on LaMnPO$_{1-x}$F$_x$ and Ca$_{1-x}$La$_x$Mn$_2$Sb$_2$ via optical spectroscopy, transport, and magnetic measurements in parallel to theoretical band structure calculations. Our studies show that LaMnPO is highly resistant to electron delocalization. Likewise, in CaMn$_2$Sb$_2$, full delocalization was not attained even though a shift in the band edge was observed.