Quasi-particles and their absence in photoemission spectroscopy

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, as shown by the formal appearance of an effective impurity problem 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 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. (C) 2002 Elsevier Science Ltd. All rights reserved.