TRUNCATION OF A 2-DIMENSIONAL FERMI-SURFACE DUE TO QUASI-PARTICLE GAPFORMATION AT THE SADDLE-POINTS

We study a two-dimensional Fermi liquid with a Fermi surface containin g the saddle points (pi, 0) and (0, pi). Including Cooper and Peierls channel contributions leads to a one-loop renormalization group flow t o strong coupling for short range repulsive interactions. In a certain parameter range the characteristics of the fixed point, opening of a spin and charge gap, and dominant pairing correlations are similar to those of a two-leg ladder at half-filling. We argue that an increase o f the electron density leads to a truncation of the Fermi surface to o nly four disconnected arcs. [S0031-9007(98)07323-2].