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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