Emergent spin-glass state in the doped Hund's metal CsFe2As2

Abstract

Hund's metal is one kind of correlated metal, in which the electronic correlation is strongly influenced by the Hund's interaction. At high temperatures, while the charge and orbital degrees of freedom are quenched, the spin degrees of freedom can persist in terms of frozen moments. As temperature decreases, a coherent electronic state with characteristic orbital differentiation always emerges at low temperatures through an incoherent-to-coherent crossover, which has been widely observed in iron-based superconductors [e.g., iron selenides and $A{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($A=\mathrm{K}$, Rb, Cs)]. Consequently, the above frozen moments are ``screened'' by coupling to orbital degrees of freedom, leading to an emergent Fermi-liquid state. In contrast, the coupling among frozen moments should impede the formation of the Fermi-liquid state by competitive magnetic ordering, which is still unexplored in Hund's metal. Here, in the iron-based Hund's metal ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$, we adopt a chemical substitution at iron sites by Cr/Co atoms to explore the competitive magnetic ordering. By a comprehensive study of resistivity, magnetic susceptibility, specific heat, and nuclear magnetic resonance, we demonstrate that the Fermi-liquid state is destroyed in Cr-doped ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$ by a spin-freezing transition below ${T}_{g}\ensuremath{\sim}22$ K. Meanwhile, the evolution of charge degrees of freedom measured by angle-resolved photoemission spectroscopy also supports the competition between the Fermi-liquid state and spin-glass state.