Realization of a Tunable Artificial Atom at a Supercritically Charged Vacancy in Graphene

TL;DR

This paper demonstrates that a single vacancy in graphene can host a tunable, supercritically charged state resembling an artificial atom, controllable via STM voltage pulses and gate tuning, with potential for electron manipulation.

Contribution

It introduces a method to create and control a supercritical charge state at a graphene vacancy, forming a tunable artificial atom with observable quasi-bound states.

Findings

Supercritical charge state can be stably hosted at a graphene vacancy.

Quasi-bound electron states resemble an artificial atom.

The trapping mechanism is gate tunable and controllable.

Abstract

The remarkable electronic properties of graphene have fueled the vision of a graphene-based platform for lighter, faster and smarter electronics and computing applications. One of the challenges is to devise ways to tailor its electronic properties and to control its charge carriers. Here we show that a single atom vacancy in graphene can stably host a local charge and that this charge can be gradually built up by applying voltage pulses with the tip of a scanning tunneling microscope (STM). The response of the conduction electrons in graphene to the local charge is monitored with scanning tunneling and Landau level spectroscopy, and compared to numerical simulations. As the charge is increased, its interaction with the conduction electrons undergoes a transition into a supercritical regime 6-11 where itinerant electrons are trapped in a sequence of quasi-bound states which resemble an artificial atom. The quasi-bound electron states are detected by a strong enhancement of the density of states (DOS) within a disc centered on the vacancy site which is surrounded by halo of hole states. We further show that the quasi-bound states at the vacancy site are gate tunable and that the trapping mechanism can be turned on and off, providing a new mechanism to control and guide electrons in graphene