Quasi-particles and their absence in photoemission spectroscopy

TL;DR

This paper reviews theoretical concepts and experimental photoemission spectra related to the formation and absence of Landau Fermi liquid quasi-particles in various strongly correlated electron systems, highlighting key paradigms like Kondo physics and Luttinger liquids.

Contribution

It provides an overview of quasi-particle formation and absence in correlated systems, contrasting Kondo physics with Luttinger liquid behavior, supported by spectral examples.

Findings

Quasi-particles form via Fermi level resonance in Kondo systems.

Quasi-particle absence is exemplified by Luttinger liquid physics.

Photoemission spectra illustrate these contrasting behaviors.

Abstract

The elucidation of Landau Fermi liquid quasi-particles and their absence in strongly correlated electron systems lies at the heart of modern research on the quantum mechanics of electrons in condensed matter. Photoemission spectroscopy of the single particle spectral function is a central experimental tool for such studies. A general paradigm of quasi-particle formation is the Fermi level resonance associated with the Kondo physics of the Anderson impurity model, an effective self consisent version of which is utilized in dynamic mean field theories of general lattice systems which may or may not literally display Kondo physics. A general paradigm of quasi-particle absence is the Luttinger liquid physics of the Tomonaga-Luttinger model. This paper presents an overview of the theoretical ideas and shows examples in photoemission spectra, taken from the work of the author and his collaborators, of quasi-particle formation in impurity and lattice Kondo and non-Kondo correlated electron systems, contrasted with quasi-particle absence in a quasi-one-dimensional system.