  Point-contact Andreev reflection spectroscopy (PCAR) has proven to be one of
the most powerful tools in the investigation of superconductors, where it
provides information on the order parameter (OP), a fundamental property of the
superconducting state. In the past 20 years, successive improvements of the
models used to analyze the spectra have continuously extended its capabilities,
making it suited to study new superconductors with "exotic" properties such as
anisotropic, nodal and multiple OPs. In Fe-based superconductors, the complex
compound- and doping-dependent Fermi surface and the predicted sensitivity of
the OP to fine structural details present unprecedent challenges for this
technique. Nevertheless, we show here that PCAR measurements in Fe-based
superconductors carried out so far have already greatly contributed to our
understanding of these materials, despite some apparent inconsistencies that
can be overcome if a homogeneous treatment of the data is used. We also
demonstrate that, if properly extended theoretical models for Andreev
reflection are used, directional PCAR spectroscopy can provide detailed
information not only on the amplitude and symmetry of the OPs, but also on the
nature of the pairing boson, and even give some hints about the shape of the
Fermi surface.
