# Uncovering Non-Fermi-Liquid Behavior in Hund Metals: Conformal Field Theory Analysis of an SU(2)×SU(3) Spin-Orbital Kondo Model

Phys. Rev. X 10, 031052 (2020)

Authors/Editors: |
E. Walter K. M. Stadler S.-S. B. Lee Y. Wang G. Kotliar A. Weichselbaum J. von Delft |
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Publication Date: | 2020 |

Type of Publication: | Articles |

Hund metals have attracted attention in recent years due to their unconventional superconductivity,

which supposedly originates from non-Fermi-liquid (NFL) properties of the normal state. When studying

Hund metals using dynamical mean-field theory, one arrives at a self-consistent “Hund impurity problem”

involving a multiorbital quantum impurity with nonzero Hund coupling interacting with a metallic bath. If

its spin and orbital degrees of freedom are screened at different energy scales, T sp < T orb , the intermediate

energy window is governed by a novel NFL fixed point, whose nature had not yet been clarified. We

resolve this problem by providing an analytical solution of a paradigmatic example of a Hund impurity

problem, involving two spin and three orbital degrees of freedom. To this end, we combine a state-of-

the-art implementation of the numerical renormalization group, capable of exploiting non-Abelian

symmetries, with a generalization of Affleck and Ludwig’s conformal field theory (CFT) approach for

multichannel Kondo models. We characterize the NFL fixed point of Hund metals in detail for a Kondo

model with an impurity forming an SUð2Þ × SUð3Þ spin-orbital multiplet, tuned such that the NFL energy

window is very wide. The impurity’s spin and orbital susceptibilities then exhibit striking power-law

behavior, which we explain using CFT arguments. We find excellent agreement between CFT predictions

and numerical renormalization group results. Our main physical conclusion is that the regime of spin-

orbital separation, where orbital degrees of freedom have been screened but spin degrees of freedom

have not, features anomalously strong local spin fluctuations: the impurity susceptibility increases as

−γ

χ imp

sp ∼ ω , with γ > 1.

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