# Orbital differentiation in Hund metals

## TL;DR

This paper investigates orbital differentiation in Hund metals using a three-orbital Hubbard model and the numerical renormalization group, revealing key phenomena near the orbital-selective Mott transition.

## Contribution

It introduces a highly accurate real-frequency dynamical mean-field study of Hund metals, uncovering new insights into orbital differentiation and associated quantum phenomena.

## Key findings

- Suppressed spin coherence scale near the transition
- Emergence of a singular Fermi liquid
- Interband doublon-holon excitations

## Abstract

Orbital differentiation is a common theme in multiorbital systems, yet a complete understanding of it is still missing. Here, we consider a minimal model for orbital differentiation in Hund metals with a highly accurate method: We use the numerical renormalization group as a real-frequency impurity solver for a dynamical mean-field study of three-orbital Hubbard models, where a crystal field shifts one orbital in energy. The individual phases are characterized with dynamic correlation functions and their relation to diverse Kondo temperatures. Upon approaching the orbital-selective Mott transition, we find a strongly suppressed spin coherence scale and uncover the emergence of a singular Fermi liquid and interband doublon-holon excitations. Our theory describes the diverse polarization-driven phenomena in the $t_{2g}$ bands of materials such as ruthenates and iron-based superconductors, and our methodological advances pave the way towards real-frequency analyses of strongly correlated materials.