Wavefunction Mapping and Magnetic Field Response of Electrostatically Defined Graphene Quantum Dots
Abstract
QDs are mesoscopic objects with 3D quantum confinement, which are often called artificial atoms due to their discrete energy levels. Over the past several decades, a tremendous amount of research has been done on semiconductor QDs, which made them one of the most well-studied QD systems and a testbed for studying rich quantum phenomena that can be hosted in QD systems. But more recently, a new type of QD that is based on atomically thin graphene materials attracted the attention of the condensed matter physics community because of the unique electronic structures hosted by graphene materials. Compared to conventional semiconductor QDs, graphene QDs offer a distinctive platform to study the interplay between quantum confinement, relativistic quantum phenomena, and non-trivial band geometrical properties. Such properties cannot be investigated in conventional semiconductor QDs. During my Ph.D. study, my research focused on investigating the electronic structure and magnetic field response of these relatively new graphene QDs. To experimentally probe graphene QD states, I used an unconventional but very powerful in-situ graphene QD creation and probing technique with STM, which enabled us to gain information of graphene QD states with atomic scale spatial resolution and meV energy resolution. Such capability of our experimental approach enabled us to gain insights on graphene QD states that are out of reach with conventional electron transport measurements. In this dissertation, I will include experimental findings from four graphene QD projects that I participated in during my Ph.D. study. This includes the observation of giant orbital magnetic moments and paramagnetic shift in MLG QDs due to their relativistic nature (chapter 5), the effect of Berry curvature and Fermi surface symmetry on the spatial distribution of BLG QD wavefunctions (chapter 6), giant valley Zeeman splitting in TLG QDs due to the giant topological orbital magnetic moment hosted in this system (chapter 7), and the unambiguous direct visualization of the relativistic quantum scars in stadium shaped MLG QDs (chapter 8). These results demonstrate that unique quantum phenomena can be achieved in graphene QDs due to the interplay between quantum confinement, relativistic quantum phenomena, and non-trivial band geometrical properties.