Abstract:: Multi-orbital systems in which the presence of a large Hund’s coupling strongly influences their electronic properties are known as Hund’s metals. The general phenomenology of these type of systems (displayed by iron-based superconductors) will be presented paying special attention to one of their main features: the presence of a region of enhanced electronic compressibility happening next to the crossover between a normal and a Hund’s metal, which may have consequences for superconductivity.
Te discussion will focus on FeSe (both bulk and monolayer) and LiFeP, LiFeAs, and NaFeAs, which have been studied computationally treating dynamical electronic correlations explicitly within a slave-spin mean-field + density-functional theory scheme. A zone of enhancement of the electronic compressibility is present in the interaction-doping phase diagram of these compounds in accord with the phenomenology of Hund’s metals. These findings correlate positively with the enhancement of superconductivity by chemical doping and pressure seen in experiments for these compounds, and support the possibility that Hund’s-coupling induced many-body correlations boost superconductive pairing when the system is at the frontier between a normal and a Hund’s metal.