Scanning Tunneling Spectroscopy of Coupled Graphene Quantum Dots

In backgated graphene devices with hexagonal boron nitride (hBN) substrates, impurities in the hBN can be locally charged by applying a voltage pulse to the tip of a scanning tunneling microscope. These charges create a writeable, tunable potential landscape for the graphene charge carriers, which we use to create isolated or coupled quantum dots in graphene. Under a strong perpendicular magnetic field, the free carriers condense into Landau levels (LLs). In a single dot, the LLs form a concentric pattern of alternating compressible and incompressible strips at the Fermi energy. The incompressible strips act as tunnel barriers creating a confined, concentric quantum dot system. When two or more such dots are placed next to each other, their charges interact. Addition of carriers to the dots manifests itself as peaks in the tunneling dI/dV, which can be tracked through the space of tip position, sample bias, and backgate voltage. as. Here, we explore the interaction between the dots revealed in the avoided crossings of their two sets of peaks to examine an intricate interplay of Coloumb interaction and tunnel coupling in this novel confined electron system.