Antiferromagnetism, $f$-wave and chiral $p$-wave superconductivity in a Kagome lattice with possible application to $sd^2$-graphenes

TL;DR

This study explores electronic instabilities in a Kagome lattice with Rashba coupling, revealing antiferromagnetic order and unconventional superconductivity, including chiral p-wave states with topological properties, relevant to $sd^2$-graphenes.

Contribution

It uncovers the emergence of antiferromagnetism and novel superconducting phases, including topologically nontrivial chiral p-wave states, in a Kagome lattice with Rashba coupling at specific fillings.

Findings

Identification of $120^o$-type antiferromagnetic order.

Discovery of $f$-wave and chiral $p$-wave superconductivity.

Chiral $p$-wave state supports edge Weyl fermions with Chern number 1.

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 $120^o$-type intra-unitcell 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 $sd^2$-graphenes proposed recently.