2-PARTICLE CORRELATIONS AND ORTHOGONALITY CATASTROPHE IN INTERACTING FERMI SYSTEMS

The wave function of two fermions, repulsively interacting in the pres ence of a Fermi sea, is evaluated in detail. We consider large but fin ite systems in order to obtain an unambiguous picture of the two-parti cle correlations. As recently pointed out by Anderson, in d less than or equal to 2 dimensions the particles may be correlated even when sit uated on the Fermi surface. The ''partial exclusion principle'' for tw o particles with opposite spin on the same Fermi point is discussed, a nd related to results from the T-matrix approximation. Particles on di fferent Fermi points are shown to be uncorrelated in d > 1. Using the results for the two-particle correlations we find that the orthogonali ty effect induced by adding an extra particle to a (tentative) two-dim ensional Fermi liquid is finite.