Global Phase Diagram of a Spin-Orbital Kondo Impurity Model and the Suppression of Fermi-Liquid Scale

• Published in: Physical review letters 2020-04, Vol.124 (13), p.136406-136406, Article 136406
• Main Authors: Wang, Y, Walter, E, Lee, S-S B, Stadler, K M, von Delft, J, Weichselbaum, A, Kotliar, G
• Format: Article
• Language: English
• Subjects: Couplings; Critical point; Ferromagnetism; Field theory; Impurities; Liquid phases; Phase diagrams; Phase transitions
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.124.136406

Many correlated metallic materials are described by Landau Fermi-liquid theory at low energies, but for Hund metals the Fermi-liquid coherence scale T_{FL} is found to be surprisingly small. In this Letter, we study the simplest impurity model relevant for Hund metals, the three-channel spin-orbital Kondo model, using the numerical renormalization group (NRG) method and compute its global phase diagram. In this framework, T_{FL} becomes arbitrarily small close to two new quantum critical points that we identify by tuning the spin or spin-orbital Kondo couplings into the ferromagnetic regimes. We find quantum phase transitions to a singular Fermi-liquid or a novel non-Fermi-liquid phase. The new non-Fermi-liquid phase shows frustrated behavior involving alternating overscreenings in spin and orbital sectors, with universal power laws in the spin (ω^{-1/5}), orbital (ω^{1/5}) and spin-orbital (ω^{1}) dynamical susceptibilities. These power laws, and the NRG eigenlevel spectra, can be fully understood using conformal field theory arguments, which also clarify the nature of the non-Fermi-liquid phase.