• Glimpse inside a graphene sandwich

    From ScienceDaily@1:317/3 to All on Wed Apr 27 22:30:48 2022
    Glimpse inside a graphene sandwich

    Date:
    April 27, 2022
    Source:
    University of Innsbruck
    Summary:
    In the search for novel types of superconductors -- phases of matter
    that that conduct electric current without loss -- scientists are
    investigating materials that consist of multiple layers. A team
    has studied in detail the properties of a system of three twisted
    graphene layers and gained important insights into its properties.



    FULL STORY ==========================================================================
    In the search for novel types of superconductors -- phases of matter that
    that conduct electric current without loss -- scientists are investigating materials that consist of multiple layers. A team has studied in detail
    the properties of a system of three twisted graphene layers and gained important insights into its properties.


    ========================================================================== Since the first successful fabrication of a two-dimensional structure of
    carbon atoms about 20 years ago, graphene has fascinated scientists. A
    few years ago, researchers discovered that two layers of graphene,
    slightly twisted against each other, can conduct electric current without
    loss. In recent years, this discovery has prompted scientists to explore
    such layered materials in greater detail. A recent notable example is mirror-symmetric twisted trilayer graphene, where three layers of graphene
    are stacked with alternating twist angles. It is the first moire' system
    that can both be efficiently tuned with a perpendicular electric field
    and was demonstrated experimentally to exhibit robust superconductivity, alongside various other phases. "This establishes trilayer graphene
    as an exciting platform for complex many-body physics, but the nature
    of the observed interaction-induced insulators, semi-metals, and superconductivity remains unknown," says Mathias Scheurer from the
    Department of Theoretical Physics of the University of Innsbruck.

    In a paper published in Physical Review X, a team led by Scheurer
    numerically and analytically studied the phase diagram of this system
    for different numbers of electrons per moire' unit cell and as a
    function of electric field. "This is a very challenging problem as the
    system has both flat and highly dispersive bands," says the theoretical physicist. "Nonetheless, we managed to show that the ground state of the
    system in the absence of a field decouples into a product of the ground
    state of graphene and the ground state of twisted bilayer graphene,"
    a property that has subsequently been confirmed by experiments.

    Their results further establish the dominance of insulating and
    semi-metallic phases in the presence of an electric field which are
    unique to the trilayer system, i.e., are not realized in twisted bilayer graphene. "We are able to use our resulting phase diagram for the
    correlated normal states to constrain the form of the superconductor,"
    says Scheurer. "Among other aspects, the resulting two superconducting candidate states we get are consistent with the unexpected stability of
    the superconductor in magnetic field seen in experiment." The relevance
    of the findings for the physics of twisted trilayer graphene is further attested by a subsequent collaboration with the group of Abhay Pasupathy
    from Columbia university. In a recent paper in Science, they report
    scanning tunneling microscopy (STM) data on this system. "We show that
    the measured tunneling spectra exhibit significant interaction effects
    that can be qualitatively captured by the numerics of our work," says
    Mathias Scheurer.


    ========================================================================== Story Source: Materials provided by University_of_Innsbruck. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Maine Christos, Subir Sachdev, Mathias S. Scheurer. Correlated
    Insulators, Semimetals, and Superconductivity in Twisted
    Trilayer Graphene. Physical Review X, 2022; 12 (2) DOI:
    10.1103/PhysRevx.12.021018 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220427100605.htm

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