Mirror nesting and repulsion-induced superconductivity

Mirror nesting condition that is a rise of pair Fermi contour due to matching of some pieces of the Fermi contour and an isoline of the pair-relative-motion kinetic energy may be satisfied, at definite total pair momenta, due to special features of electron dispersion. Perfect mirror nesting results in a rise of the possibility of superconducting ordering up to arbitrary small pairing repulsive interaction strength. Due to kinematical constraints, the order parameter exists only inside some definite domain of the momentum space and changes its sign on a line belonging to this domain