Instabilities of interacting electrons on the triangular lattice

TL;DR

This paper investigates the electronic instabilities, including superconductivity and magnetism, in interacting electrons on a triangular lattice, revealing conditions under which different phases emerge, especially near Van Hove fillings.

Contribution

It applies a one-loop renormalization group analysis to identify superconducting and magnetic phases in the triangular lattice model, highlighting the role of exchange interactions and Fermi surface size.

Findings

Local interactions do not produce instabilities at small Fermi surfaces.

Antiferromagnetic exchange interactions induce d+id-wave superconductivity.

Large Fermi surfaces lead to strong coupling and magnetic ordering tendencies.

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.