several selected examples will be discussed, supplementing those presented in the neutrons sections.

[*Strength of electronic correlations*]{}. The strength of electronic correlations are often characterized via the ratio between the on-site Hubbard repulsion coupling $U$ and the bandwidth $W$ of the hole or electron carriers. Early on, it was assumed that pnictides were in the weak-interaction limit $U/W\ll 1$. However, recent investigations revealed that the electronic correlations induce large enhancements between the effective and bare electronic masses, signaling that correlation effects cannot be neglected. For instance, Haas-van Alphen experiments for KFe$_2$As$_2$ unveiled discrepancies between the band-theory calculated and observed FS’s, including a large electronic mass enhancement 3-7 caused by band narrowing [@tterashima10]. Similar ratios for the overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ copper-oxides have been reported [@pmcrourke], suggesting that the undoped parent compounds of the pnictides resemble the overdoped copper oxides.

Additional insight is provided by optical conductivity experiments, since the ratio $R$ between the experimentally measured kinetic energy and that of band-theory calculations can be measured and contrasted against other compounds [@qazilbash09]. $R\approx 1$ signals a good metal such as Ag. LaFePO presents a ratio $R\approx 0.5$ which is borderline between weak and moderate coupling. However, pnictides such as BaFe$_{2-x}T_x$As$_2$ are characterized by 