Antiferromagnetism, f-wave, and chiral p-wave superconductivity in a kagome lattice with possible application to sd2 graphenes

Abstract

We investigate the electronic instabilities in a kagome lattice with Rashba spin-orbital coupling by the unbiased singular-mode functional renormalization group. At the parent 1/3 filling, the normal state is a quantum spin Hall system. Since the bottom of the conduction band is near the van Hove singularity, the electron-doped system is highly susceptible to competing orders upon electron interactions. The topological nature of the parent system enriches the complexity and novelty of such orders. We find 120∘-type intra-unit-cell antiferromagnetic order, f-wave superconductivity, and chiral p-wave superconductivity with increasing electron doping above the van Hove point. In both types of superconducting phases, there is a mixture of comparable spin singlet and triplet components because of the Rashba coupling. The chiral p-wave superconducting state is characterized by a Chern number Z=1, supporting a branch of Weyl fermion states on each edge. The model bares close relevance to the so-called sd2 graphenes proposed recently.

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