paper

Unraveling the origin of Kondo-like behavior in the 3-electron heavy-fermion compound YFeGe

arXiv:2502.20796 · doi:10.1073/pnas.2401430121

Abstract

The heavy fermion (HF) state of -electron systems is of great current interest since it exhibits various exotic phases and phenomena that are reminiscent of the Kondo effect in -electron HF systems. Here, we present a combined infrared spectroscopy and first-principles band structure calculation study of the -electron HF compound YFeGe. The infrared response exhibits several charge-dynamical hallmarks of HF and a corresponding scaling behavior that resemble those of the -electron HF systems. In particular, the low-temperature spectra reveal a dramatic narrowing of the Drude response along with the appearance of a hybridization gap ( 50 meV) and a strongly enhanced quasiparticle effective mass. Moreover, the temperature dependence of the infrared response indicates a crossover around 100 K from a coherent state at low temperature to a quasi-incoherent one at high temperature. Despite of these striking similarities, our band structure calculations suggest that the mechanism underlying the HF behavior in YFeGe is distinct from the Kondo scenario of the -electron HF compounds and even from that of the -electron iron-arsenide superconductor KFeAs. For the latter, the HF state is driven by orbital-selective correlations due to a strong Hund's coupling. Instead, for YFeGe the HF behavior originates from the band flatness near the Fermi level induced by the combined effects of kinetic frustration from a destructive interference between the direct Fe-Fe and indirect Fe-Ge-Fe hoppings, band hybridization involving Fe and Y electrons, and electron correlations. This highlights that rather different mechanisms can be at the heart of the HF state in -electron systems.

arXiv comment11 pages, 7 figures

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