Multiorbital Hund's coupled impurity in the mixed valence regime*

Motivated by the relevance of Hund’s coupling in iron-based superconductors, we revisit the problem of a multiorbital Anderson impurity with Hund’s interaction. Using large-N and Schwinger boson techniques, we study the ground state and thermodynamic properties of this system in both integer and mixed valence regimes. The physics is characterized by the interplay of Hund’s coupling, which tends to form large moments by aligning the spins of the impurity, and the Kondo effect, which leads to the low-temperature screening of the moments. In the integer valence regime, we confirm the formation of large moments, which eventually become screened at an exponentially reduced Kondo temperature due to the so-called Schrieffer effect, and compare to previous renormalization group studies [1]. In the mixed valence regime, the Hund’s coupling gives rise to interesting physics: we explore the presence of a non-Fermi-liquid ground state and the possibility that the large moments can generate retarded on-site pairing correlations for the conduction electrons.

[1] Nevidomskyy, A.H. and Coleman, P. "Kondo resonance narrowing in d-and f-electron systems." Phys. Rev. Lett 103.14 (2009): 147205.