Anisotropic renormalization-group flow of quasiparticle weight in a two-dimensional electron system with a partially flat Fermi surface

Two-loop renormalization-group (RG) analysis for a two-dimensional electron system with a partially flat Fermi surface has been carried out. We found that the RG flow of the quasiparticle weight depends on the location of the electron wave number $\mathit{k}$ on the Fermi surface due to the kinematical restriction to the logarithmically divergent processes in the flat regions of the Fermi surface.