Quantum well states in fractured crystals of the heavy fermion material CeCoIn$_5$

TL;DR

This study reveals quantum well states in fractured CeCoIn$_5$ crystals using photoemission spectroscopy, demonstrating atomically flat thin film formation and enabling analysis of bulk electronic properties and temperature-dependent dispersion changes.

Contribution

It is the first demonstration of quantum well states in fractured heavy fermion crystals, showing that atomically flat thin films can be formed by fracturing and enabling bulk property analysis.

Findings

Quantum well states observed in fractured CeCoIn$_5$ crystals.

Thicknesses of flakes are approximately 206 and 101 Å.

Temperature-dependent dispersion change suggests Kondo hybridization.

Abstract

Quantum well states appear in metallic thin films due to the confinement of the wave function by the film interfaces. Using angle-resolved photoemission spectroscopy, we unexpectedly observe quantum well states in fractured single crystals of CeCoIn$_5$. We confirm that confinement occurs by showing that these states' binding energies are photon-energy independent and are well described with a phase accumulation model, commonly applied to quantum well states in thin films. This indicates that atomically flat thin films can be formed by fracturing hard single crystals. For the two samples studied, our observations are explained by free-standing flakes with thicknesses of 206 and 101 \r{A}. We extend our analysis to extract bulk properties of CeCoIn$_5$. Specifically, we obtain the dispersion of a three-dimensional band near the zone center along in-plane and out-of-plane momenta. We establish part of its Fermi surface, which corresponds to a hole pocket centered at $\Gamma$. We also reveal a change of its dispersion with temperature, a signature that may be caused by the Kondo hybridization.