Effective particle–hole symmetry breaking, quasi-bond state engineering and optical absorption in graphene based gated dot–ring nanostructures

Abstract

We have studied the nature and character switching of relativistic bound states in quantum dot–ring structures produced by a set of circular concentric metallic gates on a graphene sheet placed over a substrate. The structure consists of an attractive core, a repulsive barrier and an attractive rim region where the resulting potential profiles and the interaction between the graphene layer and substrate are treated within a modified Dirac Hamiltonian describing the system. Our simulations allow a microscopic mapping of the character of electron and hole quasi-particle states and, in this environment, we study the effects of mixing between states in the dot–ring structure. Unusual electronic properties are reported by the emergence of localized states in the barrier region where electrons behave like holes in the inverted well potential and, as a direct consequence, the appearance of intertwined energy levels is envisaged which are tuned by bias voltages and the effective strength of the graphene–substrate interaction. The optical selection rules and the light absorption in effective gap regions between localized carrier states have been characterized and linked to the wavefunction engineering.