• Wed. Nov 22nd, 2023

    Critical Thought

    Critical thoughts on quantum technologies

    A New Frontier: Unraveling the Microscopic Phases of Magic-Angle Twisted Bilayer Graphene

    ByThemba Hadebe

    Nov 13, 2023
    A New Frontier: Unraveling the Microscopic Phases of Magic-Angle Twisted Bilayer Graphene

    A pioneering team of scientists, led by Princeton University, has recently achieved a significant breakthrough in understanding the complex behavior of magic-angle twisted bilayer graphene (MATBG). MATBG is a remarkable two-dimensional material consisting of twisted layers of carbon atoms that has attracted widespread attention in the field of condensed matter physics.

    With the aid of cutting-edge theoretical techniques and advanced imaging technology, the researchers were able to visualize and comprehend the minute interactions of electrons that lead to the insulating quantum phase of MATBG. This represents the first time such precise visualizations have been captured, marking a major milestone in the study of this unique material. Their findings have been published in the prestigious journal Nature.

    The extraordinary properties of twisted bilayer graphene were first discovered by a team at the Massachusetts Institute of Technology (MIT) in 2018. This material exhibits superconductivity, a state in which electrons flow with zero resistance. Superconductivity is crucial for numerous electronic applications, including the development of quantum bits (qubits) for quantum computers, as well as magnetic resonance imaging (MRI) and particle accelerators.

    Since its discovery, twisted bilayer graphene has exhibited a range of intriguing quantum physical states, including insulating, magnetic, and superconducting states. However, the mechanisms behind the formation of insulating states in MATBG have remained a puzzling mystery. Solving this enigma not only advances our understanding of insulators and proximate superconductors, but also holds significance for comprehending other unconventional superconductors, such as high-temperature cuprate superconductors.

    Although physicists have been able to observe different quantum phases in MATBG, the reasons behind these phases have remained elusive. Previous experiments have successfully demonstrated the capabilities of the material, but failed to explain the underlying mechanisms driving these states.

    The recent experiment aimed to uncover the origins of these quantum phases and gain a microscopic understanding of the behavior of electrons on the atomic scale. By utilizing the scanning tunneling microscope (STM) and its ability to probe at the nanoscale, the researchers were able to capture high-resolution images and unravel the correlated states of MATBG. This powerful tool relies on the principle of quantum tunneling, where electrons tunnel between the microscope’s tip and the sample. The resulting tunneling current provides valuable insights into the atomic world of electrons, enabling the generation of precise images of materials.

    However, the success of the experiment hinged on the creation of a flawlessly pristine sample. The surface of the carbon atoms forming the twisted bilayer graphene had to be without any imperfections or flaws. This crucial step ensured accurate measurements and reliable data.

    The research carried out by the Princeton University and University of California, Berkeley team represents two years of dedicated work. Their groundbreaking study not only sheds light on the microscopic origins of quantum phases in MATBG, but also provides valuable guidance for theorists searching for undiscovered phases.


    Q: What is magic-angle twisted bilayer graphene?
    A: Magic-angle twisted bilayer graphene is a unique material composed of two layers of graphene that are twisted at a specific “magic” angle of approximately 1.1 degrees. This angle induces unusual interactions between the electrons in the graphene sheets, resulting in various quantum phases.

    Q: What are quantum phases?
    A: Quantum phases refer to different states of matter that arise from the collective behavior of quantum particles, such as electrons. These phases can exhibit unique physical properties and interactions.

    Q: What is superconductivity?
    A: Superconductivity is a state in which certain materials possess zero electrical resistance, allowing the flow of electrons without any loss of energy. This phenomenon is important for applications such as quantum computing and electrical transmission.

    – [Princeton University](https://www.princeton.edu/news/2023/07/26/visualizing-microscopic-phases-magic-angle-twisted-bilayer-graphene)