Two years ago, the discovery of high-temperature
superconductivity in iron-pnictides reshaped the landscape
of condensed matter physics. Until that time, for more than
two decades, the copper-oxide materials were the only game
in town and their mysterious properties loomed large as
perhaps the greatest intellectual challenge in our field.
Cuprates are strongly interacting systems, near to the
so-called Mott insulating limit, in which electrons are made
motionless by strong correlations, and it is currently
believed that much of their unusual behavior stems from such
correlations. In contrast, the newly discovered iron-based
high-temperature superconductors exhibit a more moderate
degree of correlations and do not appear to be near the Mott
limit. Consequently, some of their properties might be
easier to understand. In this talk, the basic ideas in
theory of iron- pnictides will be introduced and illustrated
with experimentally-relevant examples. Particular attention
will be paid to the interband resonant-pairing mechanism of
multiband superconductivity and the renormalization group
description of the underlying physics. This will be
contrasted with strongly correlated cuprates, where a
thousand fancy theoretical ideas bloom, from quantum
fluctuations to Berry phases, from gauge field theory to
AdS/CMT duality. But we will never lose touch with reality
and promise to keep a watchful eye on recent and sometimes
conflicting experiments.
