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A Spectroscopic Study of Electronic Correlations in Twisted Bilayer Graphene by Scanning Tunneling Microscopy


Choi, Youngjoon (2022) A Spectroscopic Study of Electronic Correlations in Twisted Bilayer Graphene by Scanning Tunneling Microscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ajgk-7246.


Twisted bilayer graphene around the magic angle has shown variety of correlated phases such as superconductivity, correlated insulators, and magnetism due to its flat band structure. The unconventional nature of the superconductivity and its pos- sible relation to high temperature superconductors have sparked a lot of theoretical and experimental efforts to understand the properties of the magic angle twisted bilayer graphene. While electrical transport measurements revealed the interesting phases, spectroscopic understanding is strongly needed to connect the phases with theoretical calculations. We present the spectroscopic studies of gate-tunable magic angle twisted bilayer graphene using scanning tunneling microscopy. We report that the band structure is significantly modified even at charge neutrality due to exchange interaction. We apply a perpendicular magnetic field and develop a novel method that enables scanning tunneling microscopy to reveal Landau fan diagrams. We discover topologically non-trivial states appearing at finite magnetic field, and from spectroscopy we are able to identify the mechanism. Finally, we verify inter- action driven band flattening experimentally in twisted bilayer graphene, which is responsible for creating strong correlations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:2D materials, Graphene, Moire materials, Scanning tunneling microscopy
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Nadj-Perge, Stevan
Thesis Committee:
  • Refael, Gil (chair)
  • Alicea, Jason F.
  • Hsieh, David
  • Lee, Patrick A.
  • Nadj-Perge, Stevan
Defense Date:23 August 2021
Record Number:CaltechTHESIS:09242021-222116257
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2. adapted for Chapter 3.
Choi, Youngjoon0000-0001-9783-5992
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14372
Deposited By: Youngjoon Choi
Deposited On:28 Sep 2021 16:03
Last Modified:05 Oct 2021 16:05

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