Unraveling the origin of Kondo-like behavior in the 3d-electron heavy-fermion compound YFe2Ge2
Edited by J.C. Davis, University of Oxford, Oxford, United Kingdom; received January 22, 2024; accepted August 21, 2024
Significance
We present a combined experimental and theoretical study of the optical conductivity of 3-electron compound YFeGe. Our work reveals the presence of a flat band at the Fermi level and related optical features that are typical for heavy fermion (HF) systems. However, unlike the Kondo scenario and its analog driven by strong Hund’s coupling, we obtain evidence for an alternative mechanism which accounts for the HF-like response of YFeGe in terms of the combined effects of kinetic frustration, band hybridization, and electron correlations. Our results help to unravel the origin of the HF properties of YFeGe and also provide a broad perspective on the exotic phenomena of other -electron materials with HF-like properties, like some of the iron arsenide superconductors.
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.
Data, Materials, and Software Availability
All study data are included in the article and/or SI Appendix.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No. 12274442) and the National Key Research and Development Program of China (Grant No. 2022YFA1403901), as well as by the Swiss National Science Foundation through Grants No. 200020-172611 and 200021-214905. Z.Y. and R.L. were supported by the Fundamental Research Funds for the Central Universities (Grant No. 2243300003), the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302800), and the National Natural Science Foundation of China (Grant No. 12074041). The DFT+DMFT calculations were carried out with high-performance computing cluster of Beijing Normal University in Zhuhai. J.Z. was supported by the Key Program of National Natural Science Foundation of China (Grant No. 12234006), National Key Research and Development Program of China (Grant No. 2022YFA14032), and the Innovation Program for Quantum Science and Technology (Grant No. 2024ZD0300103). H.W. was supported by the Youth Foundation of the National Natural Science Foundation of China (Grant No. 12204108).
Author contributions
B.X. and C.B. designed research; B.X., R.L., H.W., Z.L., S.Y., C.L., J.Z., X.Q., and Z.Y. performed research; B.X., Z.Y., and C.B. analyzed data; and B.X. and C.B. wrote the paper.
Competing interests
The authors declare no competing interest.
Supporting Information
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Cover image: Pictured are rescue tigers (Panthera tigris) at In-Sync Exotics Wildlife Rescue and Educational Center in Wylie, Texas. Ellie Armstrong, Jazlyn Mooney et al. explored the genomic diversity of the privately owned captive tiger population in the United States based on genomic sequencing of 138 individuals. The study population had ancestry from all six extant wild tiger subspecies and measures of genetic diversity and inbreeding that were comparable to wild tiger populations. The results could help inform tiger conservation efforts and illegal trafficking investigations. See the article by Armstrong, Mooney et al. e2402924121. Image credit: Keri Ostermann (In-Sync Exotics Wildlife Rescue and Educational Center, Wylie, TX).
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Copyright © 2024 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).
Data, Materials, and Software Availability
All study data are included in the article and/or SI Appendix.
Submission history
Received: January 22, 2024
Accepted: August 21, 2024
Published online: September 19, 2024
Published in issue: September 24, 2024
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Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No. 12274442) and the National Key Research and Development Program of China (Grant No. 2022YFA1403901), as well as by the Swiss National Science Foundation through Grants No. 200020-172611 and 200021-214905. Z.Y. and R.L. were supported by the Fundamental Research Funds for the Central Universities (Grant No. 2243300003), the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302800), and the National Natural Science Foundation of China (Grant No. 12074041). The DFT+DMFT calculations were carried out with high-performance computing cluster of Beijing Normal University in Zhuhai. J.Z. was supported by the Key Program of National Natural Science Foundation of China (Grant No. 12234006), National Key Research and Development Program of China (Grant No. 2022YFA14032), and the Innovation Program for Quantum Science and Technology (Grant No. 2024ZD0300103). H.W. was supported by the Youth Foundation of the National Natural Science Foundation of China (Grant No. 12204108).
Author Contributions
B.X. and C.B. designed research; B.X., R.L., H.W., Z.L., S.Y., C.L., J.Z., X.Q., and Z.Y. performed research; B.X., Z.Y., and C.B. analyzed data; and B.X. and C.B. wrote the paper.
Competing Interests
The authors declare no competing interest.
Notes
This article is a PNAS Direct Submission.
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