DMFT+NRG study of spin-orbital separation in a three-band Hund's metal

TL;DR

This paper demonstrates that NRG is an effective impurity solver for DMFT, revealing detailed spectral features and spin-orbital separation in a three-band Hund's metal model at low energies and temperatures.

Contribution

It introduces the use of NRG as a multi-band impurity solver for DMFT, providing high-resolution spectral analysis of Hund's metals with novel insights into spin-orbital separation.

Findings

NRG provides unprecedented real-frequency spectral resolution at low energies.

The ground state of the model is a Fermi liquid with particle-hole asymmetry.

Spin and orbital degrees of freedom are separated, with different screening energy scales.

Abstract

We show that the numerical renormalization group (NRG) is a viable multi-band impurity solver for Dynamical Mean Field Theory (DMFT), offering unprecedent real-frequency spectral resolution at arbitrarily low energies and temperatures. We use it to obtain a numerically exact DMFT solution to the Hund's metal problem for a three-orbital model with filling factor $n_d=2$. The ground state is a Fermi liquid. The one-particle spectral function has a strong particle-hole asymmetry, with a clear apparent power law for positive frequencies only. With increasing temperature it shows a coherence-incoherence crossover with spectral weight transfered from low to high energies and evolves qualitatively differently from a doped Mott insulator. The spin and orbital spectral functions show "spin-orbital separation": spin screening occurs at much lower energies than orbital screening. The renormalization group flows clearly reveal the relevant physics at all energy scales.