Remnant Fermi surfaces in cuprates

We investigate a new methodology proposed by Ronning et al. for analyzing t he angle resolved photoernission data on high Tc cuprates - the remnant Fer mi surface (rFs). This is the locus of the points in k-space where the mome ntum distribution n(k) is one half, and can be determined even in strongly correlated electron systems that lack the Fermi surface. There are two fund amentally different classes of remnant Fermi surfaces depending on whether the interaction leads to pairing or to a generalized nesting (magnetic or c harge) instability. For pairing the remnant Fermi surface follows faithfull y the Fermi surface, whereas for magnetic or charge instabilities the rFs m aps the corresponding superlattice Brillouin zone. We exemplify these conce pts by determining the rFs for a particular model presenting two phases: fl ux phase (nesting) and d-wave superconductivity (pairing).