Remnant fermi surfaces in photoemission

Recent experiments have introduced a new concept for analyzing the photoemission spectra of correlated electrons-the remnant Fermi surface (rFs), which can be measured even in systems which lack a conventional Fermi surface. Here, we analyze the rFs in a number of interacting electron models, and find that the results fall into two classes. For systems with particle-particle (pairing) instabilities, the rFs is an accurate replica of the true Fermi surface. In the presence of particle-hole (nesting) instabilities, the rFs is a map of the resulting superlattice Brillouin zone. The results suggest that the gap in Ca2CuO2Cl2 is of particle-hole origin.