Strongly interacting
fermions govern the physics of e.g. high-temperature
superconductors, nuclear matter
and
neutron stars. The interplay of the Pauli principle with
strong interactions can give rise to exotic
properties
that we do not even understand at a qualitative level. In
recent years, ultracold Fermi gases of atoms
have
emerged as a pristine platform for the creation and study of
strongly interacting systems of fermions.
Near
Feshbach resonances, such gases display superfluidity at 17%
of the Fermi temperature. Scaled to the density
of
electrons in solids, this corresponds to superfluidity far
above room temperature. Confined in optical
lattices,
fermionic atoms realize the Fermi-Hubbard model, believed to
capture the essence of cuprate high-temperature
superconductors. In recent experiments on two-dimensional
Fermi gases under a microscope, we observe metallic,
Mott insulating and band insulating states with single-site,
single-atom resolution. The microscope allows
for
the site-resolved detection of charge and spin correlations,
revealing the famous Pauli and correlation hole
for
low and intermediate lattice fillings, and correlated
doublon-hole pairs near half filling. These
correlations
should play an important role for transport in the
Fermi-Hubbard model.
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