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

摘要

Using the variational cluster approximation (VCA) and the clusterperturbation theory, we study the finite temperature phase diagram of ahalf-depleted periodic Anderson model on the honeycomb lattice at half fillingfor a model of graphone, i.e., single-side hydrogenated graphene. The groundstate of this model is found to be ferromagnetic (FM) semi-metal. The spin wavedispersion in the FM state is linear in momentum at zero temperature butbecomes quadratic at finite temperatures, implying that the FM state is fragileagainst thermal fluctuations. Indeed, our VCA calculations find that theparamagnetic (PM) state dominates the finite temperature phase diagram. Moresurprisingly, we find that massless Dirac quasiparticles with the linear energydispersion 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 tobe highly correlated to the quasiparticle weight of the emergent massless Diracquasiparticles at the Fermi energy and monotonically increases with $U$. Theseunexpected massless Dirac quasiparticles are also examined with the Hubbard-Iapproximation and the origin is discussed in terms of the spectral weightredistribution involving a large energy scale of $U$. Considering an effectivequasiparticle Hamiltonian which reproduces the single-particle excitationsobtained by the Hubbard-I approximation, we argue that the massless Diracquasiparticles are protected by the electron correlation. Our finding istherefore the first example of the emergence of massless Dirac quasiparticlesdue to dynamical electron correlations without breaking any spatial symmetry.The experimental implications of our results for graphone as well as a graphenesheet on transition metal substrates are also briefly discussed.