Emergent Kondo Lattice Behavior in Iron-Based Superconductors AFe2As2 (A= K, Rb, Cs)

Abstract

Here, we experimentally study the origin of d-electron heavy fermion (HF) behavior in iron-based superconductors (FeSCs) AFe2As2 (A=K, Rb, Cs). Nuclear magnetic resonance on As75 reveals a universal coherent-incoherent crossover with a characteristic temperature T∗. Below T∗, a so-called "Knight shift anomaly" is first observed in FeSCs, which exhibits a scaling behavior similar to f-electron HF materials. Furthermore, the scaling rule also regulates the manifestation of magnetic fluctuation. These results undoubtedly support an emergent Kondo lattice scenario for the d-electron HF behavior, which qualifies the AFe2As2 (A=K, Rb, Cs) as d-electron HF superconductors.