UNCERTAINTY PRINCIPLE ENHANCED PAIRING CORRELATIONS IN PROJECTED FERMI SYSTEMS NEAR FILLING

We point out the curious phenomenon of order by projection in a class of lattice Fermi systems near half filling. Enhanced pairing correlati ons of extended s-wave Cooper pairs result from the process of project ing out s-wave Cooper pairs, with negligible effect on the ground-stat e energy. The Hubbard model is a particularly nice example of the abov e phenomenon, which is revealed with the use of rigorous inequalities including the uncertainty principle inequality. In addition, we presen t numerical evidence that at half filling a related but simplified mod el shows off-diagonal long range order (ODLRO) of extended s-wave Coop er pairs.