Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2023)

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.

    Cover page: Wavefunction Mapping and Magnetic Field Response of Electrostatically Defined Graphene Quantum DotsCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2023)
    Materials such as graphene and topological insulators host massless Dirac fermions that enable the study of relativistic quantum phenomena. Single quantum dots and coupled quantum dots formed with massless Dirac fermions can be viewed as artificial relativistic atoms and molecules, respectively. Such structures offer a unique testbed to study atomic and molecular physics in the ultrarelativistic regime (particle speed close to the speed of light). Here we use a scanning tunnelling microscope to create and probe single and coupled electrostatically defined graphene quantum dots to unravel the magnetic-field responses of artificial relativistic nanostructures. We observe a giant orbital Zeeman splitting and orbital magnetic moment up to ~70 meV T-1 and ~600μB (μB, Bohr magneton) in single graphene quantum dots. For coupled graphene quantum dots, Aharonov-Bohm oscillations and a strong Van Vleck paramagnetic shift of ~20 meV T-2 are observed. Our findings provide fundamental insights into relativistic quantum dot states, which can be potentially leveraged for use in quantum information science.
      Cover page: Giant orbital magnetic moments and paramagnetic shift in artificial relativistic atoms and moleculesCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2021)
      Experimental realizations of graphene-based stadium-shaped quantum dots (QDs) have been few and have been incompatible with scanned probe microscopy. Yet, the direct visualization of electronic states within these QDs is crucial for determining the existence of quantum chaos in these systems. We report the fabrication and characterization of electrostatically defined stadium-shaped QDs in heterostructure devices composed of monolayer graphene (MLG) and bilayer graphene (BLG). To realize a stadium-shaped QD, we utilized the tip of a scanning tunneling microscope to charge defects in a supporting hexagonal boron nitride flake. The stadium states visualized are consistent with tight-binding-based simulations but lack clear quantum chaos signatures. The absence of quantum chaos features in MLG-based stadium QDs is attributed to the leaky nature of the confinement potential due to Klein tunneling. In contrast, for BLG-based stadium QDs (which have stronger confinement) quantum chaos is precluded by the smooth confinement potential which reduces interference and mixing between states.
        Cover page: Imaging Quantum Interference in Stadium-Shaped Monolayer and Bilayer Graphene Quantum DotsCreative Commons 'BY-NC' version 4.0 license
        Top