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

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.