  The effect of a Zeeman magnetic field coupled to the spin of the electrons on
the conducting properties of the disordered Hubbard model is studied. Using the
Determinant Quantum Monte Carlo method, the temperature- and magnetic-field-
dependent conductivity is calculated,as well as the degree of spin
polarization. We find that the Zeeman magnetic field suppresses the metallic
behavior present for certain values of interaction- and disorder- strength, and
is able to induce a metal-insulator transition at a critical field strength. It
is argued that the qualitative features of magnetoconductance in this
microscopic model containing both repulsive interactions and disorder are in
agreement with experimental findings in two-dimensional electron- and
hole-gases in semiconductor structures.

Strongly Correlated Electrons;Disordered Systems and Neural Networks