We define a general strategy for finding new heavy-fermionic materials without rare-earth elements: doping a Hund metal with pronounced orbital-selective correlations towards half-filling. We argue that in general band structures a possible orbital-selective Mott transition is frustrated by inter-orbital hopping into heavy-fermion behaviour - where d-orbitals provide both the heavy and the light electrons - which is enhanced when approaching half-filling. This phase ultimately disappears due to magnetic correlations, as in a standard Doniach diagram. Experimentally we have further hole doped CsFe2As2, a Hund metal with 0.5 electrons/Fe away from half-filling, and obtained a heavy fermionic state with the highest Sommerfeld coefficient for Fe-pnictides to date (270 mJ/mol K2), before signatures of an antiferromagnetic phase set in.
@article{arxiv.2312.06511,
title = {Paradigm for finding d-electron heavy fermions: the case of Cr-doped CsFe$_2$As$_2$},
author = {Matteo Crispino and Pablo Villar Arribi and Anmol Shukla and Frédéric Hardy and Amir-Abbas Haghighirad and Thomas Wolf and Rolf Heid and Christoph Meingast and Tommaso Gorni and Adolfo Avella and Luca de' Medici},
journal= {arXiv preprint arXiv:2312.06511},
year = {2023}
}