Nesting induced precursor effects: A renormalization group approach

We develop a controlled weak coupling renormalization group (RG) approach t o itinerant electrons. Within this formalism we rederive the phase diagram for two-dimensional non-nested systems. We then study how nesting modifies this phase diagram. We show that competition between particle-particle and particle-hole channels leads to the manifestation of an unstable precursor fixed point in the RG flow. This effect should be experimentally measurable , and may be relevant for an explanation of pseudogaps in the high temperat ure superconductors, as a crossover phenomenon.