Ferromagnetism and Wigner crystallization in Kagome graphene and related structures

TL;DR

This paper proposes real-atom Kagome graphene structures that exhibit flat bands, enabling the realization of ferromagnetism and Wigner crystallization through doping, with potential for experimental synthesis.

Contribution

It introduces Kagome graphene/graphyne as a realistic platform for flat band physics, demonstrating ferromagnetism and Wigner crystallization via density functional theory calculations.

Findings

Flat bands near the Fermi level in Kagome lattices.

Hole doping induces spin-polarized ferromagnetism.

Wigner crystal formation at specific fillings.

Abstract

Interaction in a flat band is magnified due to the divergence in the density of states, which gives rise to a variety of many-body phenomena such as ferromagnetism and Wigner crystallization. Until now, however, most studies of the flat band physics are based on model systems, making their experimental realization a distant future. Here, we propose a class of systems made of real atoms, namely, carbon atoms with realistic physical interactions (dubbed here as Kagome graphene/graphyne). Density functional theory calculations reveal that these Kagome lattices offer a controllable way to realize robust flat bands sufficiently close to the Fermi level. Upon hole doping, they split into spin-polarized bands at different energies to result in a flat-band ferromagnetism. At a half filling, this splitting reaches its highest level of 768 meV. At smaller fillings, e.g., when {\nu}=1/6, on the other hand, a Wigner crystal spontaneously forms, where the electrons form closed loops localized on the grid points of a regular triangular lattice. It breaks the translational symmetry of the original Kagome lattice. We further show that the Kagome lattices exhibit good mechanical stabilities, based on which a possible route for experimental realization of the Kagome graphene is also proposed.