Duality of deconfined quantum critical point in two dimensional Dirac semimetals

TL;DR

This paper explores the quantum criticality and duality between Néel and Kekulé valence bond solid phases in graphene Dirac semimetals, revealing a deconfined quantum critical point with emergent phenomena and topological features.

Contribution

It introduces a comprehensive analysis of the Néel-Kekulé transition, highlighting the duality, multicriticality, and topological aspects within a continuum field theory framework.

Findings

Identification of a mutual-duality between Néel and Kekulé VBS orders.

Evidence of a deconfined quantum critical point with emergent spinons.

Connection between topological defects and zero-energy modes in Kekulé phase.

Abstract

In this paper we discuss the N$\acute{e}$el and Kekul$\acute{e}$ valence bond solids quantum criticality in graphene Dirac semimetal. Considering the quartic four-fermion interaction $g(\bar{\psi}_i\Gamma_{ij}\psi_j)^2$ that contains spin,valley, and sublattice degrees of freedom in the continuum field theory, we find the microscopic symmetry is spontaneously broken when the coupling $g$ is greater than a critical value $g_c$. The symmetry breaking gaps out the fermion and leads to semimetal-insulator transition. All possible quartic fermion-bilinear interactions give rise to the uniform critical coupling, which exhibits the multicritical point for various orders and the Landau-forbidden quantum critical point. We also investigate the typical critical point between N$\acute{e}$el and Kekul$\acute{e}$ valence bond solid transition when the symmetry is broken. The quantum criticality is captured by the Wess-Zumino-Witten term and there exist a mutual-duality for N$\acute{e}$el-Kekul$\acute{e}$ VBS order. We show the emergent spinon in the N$\acute{e}$el-Kekul$\acute{e}$ VBS transition , from which we conclude the phase transition is a deconfined quantum critical point. Additionally, the connection between the index theorem and zero energy mode bounded by the topological defect in the Kekul$\acute{e}$ VBS phase is studied to reveal the N$\acute{e}$el-Kekul$\acute{e}$ VBS duality.