Hund’s physics-driven strong correlation in the altermagnet CaCrO3

Altermagnetism has attracted intense interest, but strong correlation effects in altermagnets remain largely unexplored. Here, using density functional theory plus dynamical mean-field theory (DFT + DMFT), we identify CaCrO 3 , a rare example of a correlated metallic altermagnet with substantial Hund’s coupling. We show that Hundness leads to incoherent metallicity with altermagnetic spin splitting and sustains local spin moments. The DFT + DMFT-calculated magnetic moment (~ 1.3 µ B /Cr) is in quantitative agreement with neutron diffraction (~ 1.2 µ B /Cr), while conventional DFT + U predicts an insulating state instead. Furthermore, Hundness promotes incipient flat bands and gives rise to heavy-fermion-like behavior in this 3 d system, with effective mass enhancement m * / m ~ 47. This work demonstrates DFT + DMFT as a reliable computational tool for studying strongly correlated altermagnets and highlights the importance of Hund’s physics in these emerging materials.