Prof. Seung-Sup Lee

Two-stage screening in Hund metals and heavy fermions

The dynamical mean-field theory (DMFT) framework has been successful in understanding the physics of strongly correlated metals in terms of the Kondo screening, in that local fluctuations of different degrees of freedom (spin, orbital, etc.) are screened by surrounding electrons. In this presentation, I will show that Hund metals [1-4] and heavy-fermion systems [5], two seemingly distinct classes of materials, exhibit a common phenomenon of the two-stage Kondo screening, yet different degrees of freedom are involved. The screening picture explains the smallness of the Fermi-liquid coherence scales of these systems as well as the non-Fermi liquid regime appearing at intermediate energies between the two screening energy scales. Moreover, I will show that the two-stage screening picture resolves open questions in heavy-fermion systems.

[1] F. B. Kugler, S.‑S. B. Lee, A. Weichselbaum, G. Kotliar, and J. von Delft, Orbital differentiation in Hund metals, Phys. Rev. B 100, 115159 (2019).

[2] F. B. Kugler, M. Zingl, H. U. R. Strand, S.‑S. B. Lee, J. von Delft, and A. Georges, Strongly Correlated Materials from a Numerical Renormalization Group Perspective: How the Fermi-Liquid State of Sr2 RuO4 Emerges, Phys. Rev. Lett. 124, 016401 (2020).

[3] Y. Wang, E. Walter, S.‑S. B. Lee, K. M. Stadler, J. von Delft, A. Weichselbaum, and G. Kotliar, Global Phase Diagram of a Spin-Orbital Kondo Impurity Model and the Suppression of Fermi‑Liquid Scale, Phys. Rev. Lett. 124, 136406 (2020).

[4] E. Walter, K. M. Stadler, S.‑S. B. Lee, Y. Wang, G. Kotliar, A. Weichselbaum, and J. von Delft, 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).

[5] A. Gleis, S.-S. B. Lee, A. Weichselbaum, G. Kotliar, and J. von Delft, in preparation.

Dynamical susceptibilities in a Hund metal and a heavy-fermion system reveal underlying two-stage screening in both systems.