Valence Bond Order and Antiferromagnetism in Silicene - ab initio Results

TL;DR

This paper uses ab initio calculations to show that silicene exhibits valence bond order and antiferromagnetism, supporting the idea that it has a Mott insulator ground state due to strong electron correlations.

Contribution

It provides the first ab initio evidence of valence bond dimerization and antiferromagnetic order in silicene, indicating Mott localization.

Findings

Silicene shows Kekule valence bond order.

Silicene exhibits weak two-sublattice antiferromagnetism.

Evidence supports Mott insulator behavior in silicene.

Abstract

Silicene and Graphene are similar and have $\pi$-$\pi^*$ bands. However band width in silicene is only a third of graphene. It results in a substantial increase in the ratio of Hubbard U to band width W, U/W $\sim$ 0.5 in graphene to $\sim 1$ in silicene. This enhancement, 2 dimensionality and phenomenology suggest a Mott insulator based ground state for silicene (G. Baskaran, arXiv:1309.2242). We lend support to the above proposal by showing, in an ab-initio calculation, that unlike graphene, silicene has two instabilities: i) a valence bond (Kekule) dimerization and ii) a weak two sublattice antiferromagnetic order. Presence of these instabilities, in the absence of fermi surface nesting, point to Mott localization, \textit{within the frame work of ab-initio scheme}. Substrate dependent structural reconstructions seen experimentally in silicene are interpreted as generalized Kekule bond order.