  Based on the thermodynamic Green function approach two-nucleon correlations
in nuclear matter at finite temperatures are revisited. To this end, we derive
phase equivalent effective $r$-space potentials that include the effect of the
Pauli blocking at a given temperature and density. These potentials enter into
a Schr\"odinger equation that is the $r$-space representation of the
Galitskii-Feynman equation for two nucleons. We explore the analytical
structure of the equation in the complex $k$-plane by means of Jost functions.
We find that despite the Mott effect the correlation with deuteron quantum
numbers are manifested as antibound states, i.e., as zeros of the Jost function
on the negative imaginary axis of the complex momentum space. The analysis
presented here is also suited for Coulombic systems.
