Emergence of massless Dirac quasiparticles in correlated hydrogenated graphene with broken sublattice symmetry

TL;DR

This paper demonstrates that strong electron correlations in hydrogenated graphene can induce massless Dirac quasiparticles without breaking spatial symmetry, revealing a novel correlation-driven topological feature.

Contribution

It uncovers the emergence of massless Dirac quasiparticles driven by electron correlations in a correlated honeycomb lattice system, without symmetry breaking.

Findings

Massless Dirac quasiparticles appear at the Fermi energy with increasing correlation U.

Dirac Fermi velocity correlates with quasiparticle weight and increases with U.

The Dirac quasiparticles are protected by electron correlation effects.

Abstract

Using the variational cluster approximation (VCA) and the cluster perturbation theory, we study the finite temperature phase diagram of a half-depleted periodic Anderson model on the honeycomb lattice at half filling for a model of graphone, i.e., single-side hydrogenated graphene. The ground state of this model is found to be ferromagnetic (FM) semi-metal. The spin wave dispersion in the FM state is linear in momentum at zero temperature but becomes quadratic at finite temperatures, implying that the FM state is fragile against thermal fluctuations. Indeed, our VCA calculations find that the paramagnetic (PM) state dominates the finite temperature phase diagram. More surprisingly, we find that massless Dirac quasiparticles with the linear energy dispersion emerge at the Fermi energy upon introducing the electron correlation $U$ at the impurity sites in the PM phase. The Dirac Fermi velocity is found to be highly correlated to the quasiparticle weight of the emergent massless Dirac quasiparticles at the Fermi energy and monotonically increases with $U$. These unexpected massless Dirac quasiparticles are also examined with the Hubbard-I approximation and the origin is discussed in terms of the spectral weight redistribution involving a large energy scale of $U$. Considering an effective quasiparticle Hamiltonian which reproduces the single-particle excitations obtained by the Hubbard-I approximation, we argue that the massless Dirac quasiparticles are protected by the electron correlation. Our finding is therefore the first example of the emergence of massless Dirac quasiparticles due to dynamical electron correlations without breaking any spatial symmetry. The experimental implications of our results for graphone as well as a graphene sheet on transition metal substrates are also briefly discussed.