Hund-enhanced electronic compressibility in LiFeP, LiFeAs and NaFeAs tuned by chemical substitution*

We study the electronic structure of LiFeP, LiFeAs and NaFeAs in their paramagnetic metallic phase including dynamical electronic correlations within a density functional theory + slave-spin mean-field framework. Our results show that the three compounds are next to the crossover between a normal and a Hund’s metal, where a region of enhanced electronic compressibility that may be relevant for superconductivity is present in this type of systems. While LiFeP and LiFeAs lie in the normal metallic regime, with LiFeAs in the vicinity of the crossover, NaFeAs is in the Hund’s metal regime, which explains the different behavior observed in these materials. Our findings correlate positively with the experimental trends for doping- and pressure-dependence of superconductivity in these compounds, as well as the predicted mass renormalizations and Sommerfeld coefficients.