Emergent Kondo scaling in iron-based superconductors AFe2As2 (A = K, Rb, Cs)

TL;DR

This study reveals Kondo-like heavy fermion behavior in iron-based superconductors without f-electrons, demonstrating a universal crossover and scaling behavior similar to f-electron systems, and proposing these materials as d-electron HF superconductors.

Contribution

It provides experimental evidence of emergent Kondo physics in d-electron iron-based superconductors, expanding the understanding of heavy fermion phenomena beyond f-electron systems.

Findings

Universal coherent-incoherent crossover at temperature T*

Observation of Knight shift anomaly with scaling behavior

Support for emergent Kondo scenario in d-electron systems

Abstract

Unconventional superconductivity from heavy fermion (HF) is always observed in f-electron systems, in which Kondo physics between localized f-electrons and itinerant electrons plays an essential role. Whether HF superconductivity could be achieved in other systems without f electrons, especially for d-electron systems, is still elusive. Here, we experimentally study the origin of d-electron HF behavior in iron-based superconductors (FeSCs) AFe2As2 (A = K, Rb, Cs). Nuclear magnetic resonance on 75As 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 scenario for the d-electron HF behavior, which suggests the AFe2As2 (A = K, Rb, Cs) as the first material realization of d-electron HF superconductors.