Correlations and their orbital selectivity in Fe-based superconductors: from light to heavy fermions.

Fe-based superconductors typically show Fermi-liquid behaviour at low temperature in their normal state. However, across their families electronic correlations can be shown to go from weak to extremely strong, and from uniform to orbitally-selective. High-Tc superconductivity is found away from these two extreme limits, showing that correlations most likely play a delicate role in enhancing it.

These materials also provide a paradigmatic strategy for reproducing and studying heavy-fermion physics within d-element compounds.