Characterization and Control of Dirac Fermions Within Nanoscale p-n Junctions

Dirac fermions have coexisting electron-hole states and exhibit angular anisotropy when transmitting through a potential barrier. Because of these attributes, electrostatically confined Dirac fermions are fundamentally different from similarly trapped Schrödinger fermions and are predicted to exhibit new states. Such states have properties that depend on the integrability of their confinement potential and whether they are massless or massive Dirac fermions. Several recent experiments have investigated electrostatically confined states within integrable structures. However, the spatial behavior of states within non-integrable structures and of massive Dirac fermions still remains unexplored. Here, I will discuss two experiments that use scanning tunneling microscopy (STM) to characterize and manipulate Dirac fermions within circular and non-circular pn junctions. These confinement structures were fabricated by using a flexible technique for creating pn junctions on graphene/boron nitride and bilayer graphene/boron nitride heterostructures. First, I will discuss our realization of new gate tunable quantum interference patterns within circular and stadium shaped graphene pn junctions. Secondly, I will discuss our visualization and control of single electron charging events with massive Dirac fermions that are confined within circular bilayer graphene pn junctions. The techniques and findings presented here open the door to highly controlled studies on the ergodicity of confined Dirac fermions—gate tunable Dirac billiards.