  A quantum field theoretical approach to the thermodynamics of dense Fermi
systems is developed for the description of the formation and dissolution of
quantum condensates and bound states in dependence of temperature and density.
As a model system we study the chiral and superconducting phase transitions in
two-flavor quark matter within the NJL model and their interrelation with the
formation of quark-antiquark and diquark bound states. The phase diagram of
quark matter is evaluated as a function of the diquark coupling strength and a
coexistence region of chiral symmetry breaking and color superconductivity is
obtained at very strong coupling. The crossover between Bose-Einstein
condensation (BEC) of diquark bound states and condensation of diquark
resonances (Cooper pairs) in the continuum (BCS) is discussed as a Mott effect.
This effect consists in the transition of bound states into the continuum of
scattering states under the influence of compression and heating. We explain
the physics of the Mott transition with special emphasis on role of the Pauli
principle for the case of the pion in quark matter.
