  Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. The last decade witnessed significant progress in
this technique and its applications, thus ushering in a new era in
photoelectron spectroscopy; today, ARPES experiments with 2 meV energy
resolution and 0.2 degree angular resolution are a reality even for
photoemission on solids. In this paper we will review the fundamentals of the
technique and present some illustrative experimental results; we will show how
ARPES can probe the momentum-dependent electronic structure of solids providing
detailed information on band dispersion and Fermi surface, as well as on the
strength and nature of those many-body correlations which may profoundly affect
the one-electron excitation spectrum and, in turn, determine the macroscopic
physical properties.
