  Thermal properties of single species nucleon matter are investigated assuming
a simple form of the nucleon-nucleon interaction. The nucleons are placed on a
cubic lattice, hopping from site to site and interacting through a
spin-dependent force, as in the extended, attractive Hubbard model. A mean
field calculation in the Hartree-Fock Bogoliubov approximation suggests that
the superfluid ground state generated by strong nucleon pairing undergoes a
second-order phase transition to a normal state as the temperature increases.
The calculation is shown to lead to a promising description of the thermal
properties of low-density neutron matter. A possibility of a density wave phase
is also examined.
