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Visualizing the merger of tunably coupled graphene quantum dots



Daniel Walkup, Fereshte Ghahari, Steven R. Blankenship, Kenji Watanabe, Takashi Taniguchi, Nikolai Zhitenev, Joseph A. Stroscio


Coupled quantum dots have been realized in a wide variety of physical systems and have attracted interest for many different applications. Here, we examine novel graphene quantum dots in backgated devices on hBN, and visualize their merger using scanning tunneling microscopy and spectroscopy (STM/STS). These dots are formed by the combination of nanoscale potential wells created by pulsing the voltage of an STM tip above charged defects in the hBN underlayer, and strong magnetic fields gapping the density of states, adding insulating rings at the potential wells. Control of the charge state is achieved via the back gate and sample bias voltages, and the position of the STM tip which serves as a mobile top gate. The individual quantum dots present a novel phenomenology of single-electron charging due to multiple Landau levels crossing the Fermi energy concentrically. Here, we study side-by-side pairs of these quantum dots via STM, where we observe a tunable inter-dot coupling and mergeability. Specifically, with increasing charge filling, the quantum dots of one Landau level merge into a single quantum dot, while the ones in the next-higher Landau level remain separated into two charge pockets. Using the probe tip as a multi-function tool, we visualize the evolution, growth and merger of this unique DQD system as a function of tip position and gate voltages.
Physical Review B


Walkup, D. , Ghahari, F. , Blankenship, S. , Watanabe, K. , Taniguchi, T. , Zhitenev, N. and Stroscio, J. (2023), Visualizing the merger of tunably coupled graphene quantum dots, Physical Review B, [online],, (Accessed March 2, 2024)
Created December 6, 2023