  We describe baryons as quark-diquark bound states at finite temperature and
density within the NJL model for chiral symmetry breaking and restoration in
quark matter. Based on a generalized Beth-Uhlenbeck approach to mesons and
diquarks we present in a first step the thermodynamics of quark-diquark matter
which includes the Mott dissociation of diquarks at finite temperature. In a
second step we solve the Bethe-Salpeter equation for the baryon as a
quark-diquark bound state in quark-diquark matter. We obtain a stable, bound
baryon even beyond the Mott temperature for diquark dissociation since the
phase space occupation effect (Pauli blocking for quarks and Bose enhancement
for diquarks) in the Bethe-Salpeter kernel for the nucleon approximately cancel
so that the nucleon mass follows the in-medium behaviour of the quark and
diquark masses towards chiral restoration. In this situation the baryon is
obtained as a "borromean" three-quark state in medium because the two-particle
state (diquark) is unbound while the three-particle state (baryon) is bound.
