Abstract
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, , 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 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 , with .
- Received 12 August 2019
- Revised 27 May 2020
- Accepted 7 July 2020
DOI:https://doi.org/10.1103/PhysRevX.10.031052
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Erratum
Erratum: Uncovering Non-Fermi-Liquid Behavior in Hund Metals: Conformal Field Theory Analysis of an Spin-Orbital Kondo Model [Phys. Rev. X 10, 031052 (2020)]
E. Walter, K. M. Stadler, S.-S. B. Lee, Y. Wang, G. Kotliar, A. Weichselbaum, and J. von Delft
Phys. Rev. X 12, 019901 (2022)
Popular Summary
Hund metals are a broad class of materials exhibiting strong electron-electron interactions. Examples include the ruthenates and the iron pnictides, the latter being of great interest since they exhibit unconventional high-temperature superconductivity. Whereas most metals are described as Fermi liquids—in which interacting electrons collectively behave as a fluid within the material—researchers suspect that the normal state of a Hund metal is governed by a novel non-Fermi-liquid phase, which has not yet been understood in detail. Here, we provide a detailed analysis of the origin of this non-Fermi-liquid behavior.
The physics of Hund metals can essentially be described in terms of an impurity model, where the fluctuations of the spin and orbital degrees of freedom at a local site (“impurity”) are screened by surrounding electrons. A detailed understanding of the combined spin and orbital screening process has been lacking for decades. We fill this long-standing void by combining state-of-the-art numerical methods and field theory, which enables us to analytically explain striking power-law behaviors of the impurity’s spin and orbital susceptibilities, characteristic of the non-Fermi-liquid phase of Hund metals.
Our work is a paradigmatic example for bridging the gap between the material-specific high-energy properties of multiorbital systems and their emergent low-energy behavior.
