Photoelectron spectroscopy

Abstract

Most properties of materials reflect, directly or indirectly, the nature of their electronic states. Electrons interact with the ions and therefore feel the translation symmetry of the lattice but also, namely in interesting materials, with other electrons. This leads to complex correlated states. Not surprisingly, the most straightforward way to investigate electronic properties is to remove the electrons from the solid, and to measure them far from the interacting system. This is the general idea of a photoemission experiment. Perhaps more surprisingly, such a simple measurement contains crucial information on the interacting system. The purpose of this chapter is to illustrate this simple and powerful idea. The impressive results obtained over the past four decades, and the huge number of experiments performed every year, demonstrate that photoemission has reached the venerable status of a standard probe of the electronic properties of solids. And yet, new and exciting developments, often associated with synchrotron radiation, are reshaping the practice and scope of the technique, bridging the gap with conventional "thermodynamic" probes of the electronic states. The forefront of research has moved from studies of the band structure on the eV scale, to the investigation of elementary excitations, electronic instabilities, and new exotic properties of correlated systems, at the meV range and with high momentum resolution. In this perspective, this chapter gives only a very brief account of traditional aspects of photoelectron spectroscopy, while it addresses, with examples from the recent literature, the spectral properties of correlated electron systems. For a broader view and a much more detailed description of the technique the reader is referred to some excellent reviews [1,2]. This chapter is organized as follows: section 2 gives a brief qualitative description and an intuitive interpretation of a photoemission experiment. Section 3 presents a discussion of a photoemission spectrum based on the simple and widespread 3-step model. Correlation effects and their manifestation in the spectral properties are introduced in section 4. These ideas are illustrated by selected case studies in section 5. © 2006 Springer.