Angle-resolved photoemission spectroscopy
(ARPES) is one of the most direct methods of studying the electronic structure
of solids and is the only truly momentum-resolved probe, which is essential
for the investigation of low dimensional and strongly anisotropic systems.
By measuring momentum and kinetic energy of the electrons photoemitted
from a sample illuminated with radiation of energy larger than the material
work function, it is possible to gain information on both energy and the
momentum of the electronic excitations inside the solid.
As the intensity measured in photoemission
experiments is proportional to the single-particle spectral function A(k,w)=-(1/p)ImG(k,w),
ARPES provides direct insights on the Green's function G(k,w)
which describes the propagation of an electron in a many-body system. 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 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,
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.