Interplay of charge and spin fluctuations in a Hund's coupled impurity

Abstract

In Hund's metals, the local ferromagnetic interaction between orbitals leads to an emergence of complex electronic states with large and slowly fluctuating magnetic moments. Introducing a new analysis of a Hund's coupled mixed valence quantum impurity, we gain analytic insight into recent numerical renormalization group studies. We show that valence fluctuations drastically impedes the development of a large fluctuating moment over a wide swath of temperatures and energy, characterized by quenched orbital degrees of freedom and a singular logarithmic behavior of the spin susceptibility χ sp (ω) ∝ [ω log(ω/T eff K ) 2 ] −1 , closely resembling power-law scaling χ sp (ω) ∼ ω −γ . These singular spin fluctuations may play an important role in future models of Hund's driven Cooper pairing.

Triplet pairing, orbital selectivity and correlations in Iron-based superconductors

“…The value of γ = 1.2 relevant to the observed ∆/T c in FeSC occurs in DMFT solutions of Hund's metals [20,25], and (approximately) in the aforementioned SOS regime of multi-orbital [33] and mixed-valent Hund's impurities. [34] Combining experimental observations with the above-mentioned Hund's phenomenology, naturally leads to the question of investigating the possibility of triplet superconductivity in FeSC.…”