Approaching itinerant magnetic quantum criticality through a Hund's coupling induced electronic crossover in the YFe2Ge2 superconductor

Abstract

Here, by conducting a systematic Y89 NMR study, we explore the nature of the magnetic ground state in a newly discovered iron-based superconductor YFe2Ge2. An incoherent-to-coherent crossover due to the Hund's coupling induced electronic correlation is revealed below the crossover temperature T*∼75±15K. During the electronic crossover, both the Knight shift (K) and the bulk magnetic susceptibility (χ) exhibit a similar nonmonotonic temperature dependence, and a so-called Knight shift anomaly is also revealed by a careful K−χ analysis. Such an electronic crossover has been also observed in heavily hole-doped pnictide superconductors AFe2As2 (A=K, Rb, and Cs), which is ascribed to the Hund's coupling induced electronic correlation. Below T*, the spin-lattice relaxation rate divided by temperature (1/T1T) shows a similar suppression as the Knight shift, suggesting the absence of critical spin fluctuations. This seems to be in conflict with a predicted magnetic quantum critical point (QCP) near this system. However, considering a q-dependent “filter” effect on the transferred hyperfine field, a predominant spin fluctuation with A-type correlation would be perfectly filtered out at Y89 sites, which is consistent with the recent inelastic neutron scattering results. Therefore, our results confirm that, through a Hund's coupling induced electronic crossover, the magnetic ground state of YFe2Ge2 becomes close to an itinerant magnetic QCP with A-type spin fluctuations. In addition, the possible superconducting pairing due to spin fluctuations is also discussed.

Source-reported materials — not catalogue approval

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