Instabilities of interacting electrons on the triangular lattice

Abstract

Motivated by the recent finding of superconductivity in layered CoO_2 compounds, we investigate superconducting and magnetic instabilities of interacting electrons on the two-dimensional triangular lattice. Using a one-loop renormalization group scheme for weak to moderate coupling strengths, we find that for purely local interactions U>0 and small Fermi surfaces the renormalization group flow remains bounded down to very low scales and no superconducting or other instabilities can be detected. Antiferromagnetic exchange interactions J generate a wide density region with a d_{x^2-y^2}+id_{xy}-wave superconducting instability similar to recent proposals for the strongly correlated t-J model. For larger Fermi surface volumes the interactions flow to strong coupling also for purely local interactions U>0. We find a singlet pairing instability in the vicinity of strong magnetic ordering tendencies at three wavevectors for the van Hove filling.