Imaging electrostatically confined Dirac fermions in graphene quantum dots

TL;DR

This study uses STM to visualize and analyze the quantum interference and energy levels of Dirac fermions confined in graphene quantum dots created by local defect charge manipulation, providing new insights into relativistic particle confinement.

Contribution

It introduces a novel technique for fabricating graphene quantum dots via defect charge manipulation and provides detailed STM mapping of confined Dirac fermions and their interference patterns.

Findings

Observation of quasi-bound states within graphene quantum dots.

Visualization of quantum interference patterns of confined electrons.

Detection of Friedel oscillation-like behavior outside the quantum dots.

Abstract

Electrostatic confinement of charge carriers in graphene is governed by Klein tunneling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at pn junction boundaries. Reflection and transmission at these novel potential barriers should affect the quantum interference of electronic wavefunctions near these boundaries. Here we report the use of scanning tunneling microscopy (STM) to map the electronic structure of Dirac fermions confined by circular graphene pn junctions. These effective quantum dots were fabricated using a new technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe energy levels corresponding to quasi-bound states and we spatially visualize the quantum interference patterns of confined electrons. Dirac fermions outside these quantum dots exhibit Friedel oscillation-like behavior. Bolstered with a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield new insight into the spatial behavior of electrostatically confined Dirac fermions.