Pnictides at half-filling: Electronic, magnetic, and optical properties of manganese pnictides

Strong electronic correlations happen very often in open d- or f- shells close to half filling. As an example of such systems we study BaMn$_2$As$_2$ and LaOMnAs, two manganese pnictides. They are similar to the extensively studied iron pnictide high-temperature superconductors BaFe$_2$As$_2$ and LaOFeAs, but with the difference of having only 5 electrons in the d shell as compared to 6 electrons in the iron systems. Due to this half-filled situation, the manganese pnictides are candidates for the Mott insulating parent compounds, in analogy with curate superconductors.
Half-filling has important consequences, in the sense that electronic interactions are much stronger. As a result, we show that both materials are close to a Mott metal-to-insulator transition. This location in the phase diagram leads to strong magnetism, with a remarkably high Neel temperature of 625K for BaMn$_2$As$_2$. We also discuss the difference in the magnetic ordering temperatures and trace it back to the different dimensionality oft the electronic structure in these compounds. Finally, we also study the optical conductivity. The inclusion of correlation effects gives optical spectra in very good agreement, which cannot be achieved by density-functional theory calculations alone.