Unconventional superconductivity and Hund's induced electron correlations: a Cooperative mechanism*

The phenomenology of iron-based superconductors shows that the normal state is a bad metal characterized by orbital-selective correlations induced by the Hund's exchange coupling, suggesting an important role of the electron-electron interactions. On the other hand theories based on the exchange of bosons (e.g. spin fluctuations) describe correctly a variety of phenomena pointing towardsa more standard pairing mechanism.
To overcome this dychotomy we study how a multiorbital superconducting pairing driven by a generic weak-copuling boson exchange is affected by the presence of correlations. The key novelty of the study is the inclusion of the dynamical properties that make a Hund's metal substantially different with respect to both a weakly interacting metal and to an ordinary correlated metal with a large effective mass renormalization. We unveil the crucial role of the redistribution of spectral weight of the Hund’s metal to promote superconductivity and to enhance the orbital-selective character of the gap functions.