# Evolution of the Kondo lattice electronic structure above the transport coherence temperature

## TL;DR

This study combines ARPES experiments and DMFT calculations to reveal that in the Kondo lattice system CeCoIn$_5$, $f$ electrons participate in the Fermi surface at temperatures well above the coherence temperature, challenging previous assumptions.

## Contribution

It provides a microscopic understanding of the temperature evolution of $f$-$d$ hybridization and Fermi surface participation in CeCoIn$_5$, linking experimental ARPES data with realistic DMFT calculations.

## Key findings

- $f$ electrons participate in the Fermi surface above $T^*$
- Identification of a crystalline electric field degeneracy crossover below $T^*$
- ARPEs and DMFT results show temperature-dependent hybridization behavior

## Abstract

The temperature-dependent evolution of the Kondo lattice is a long-standing topic of theoretical and experimental investigation and yet it lacks a truly microscopic description of the relation of the basic $f$-$d$ hybridization processes to the fundamental temperature scales of Kondo screening and Fermi-liquid lattice coherence. Here, the temperature-dependence of $f$-$d$ hybridized band dispersions and Fermi-energy $f$ spectral weight in the Kondo lattice system CeCoIn$_5$ is investigated using $f$-resonant angle-resolved photoemission (ARPES) with sufficient detail to allow direct comparison to first principles dynamical mean field theory (DMFT) calculations containing full realism of crystalline electric field states. The ARPES results, for two orthogonal (001) and (100) cleaved surfaces and three different $f$-$d$ hybridization scenarios, with additional microscopic insight provided by DMFT, reveal $f$ participation in the Fermi surface at temperatures much higher than the lattice coherence temperature, $T^*\approx$ 45 K, commonly believed to be the onset for such behavior. The identification of a $T$-dependent crystalline electric field degeneracy crossover in the DMFT theory $below$ $T^*$ is specifically highlighted.