Hund metal is a recently coined term to refer to a special type of correlated metals in which atomic Hund interaction plays the key role [1]. In this talk, after a brief introduction to Hund metal, I will present our recent progress on this issue [2]. We conducted a detailed investigation on the two-orbital case which has been on the periphery of the attention. We identify distinctive regimes, particularly the four different correlated metals; one stems from the proximity to a Mott insulator and the other three we call ‘intermediate’ metal, ‘weak Hund’ metal, and ‘valence-skipping’ metal. Defining criteria characterizing these metals is suggested. Contrary to conventional wisdom the current study establishes the existence of Hund metallicity in two-orbital systems. Our result also provides useful insights to understand metallic two-orbital systems such as the recently discovered superconducting infinite-layer nickelates.

Reference
[1] For a review, see, A. Georges et al., Annu. Rev. Condens. Matter Phys. 4, 137 (2013).
[2] S. Ryee et al., Phys. Rev. Lett. 126, 206401 (2021)

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