highlight / actuality | scientific result
Magic angle twisted bilayer graphene has emerged in the past decade as a platform for non-conventional superconductivity. This behavior arises in the presence of a localized flat band as the twist angle approaches a well-defined value referred to as the
magic angle, shown in a pioneering theoretical work . This theoretical prediction was later confirmed by experiments , giving more details on the superconducting behavior of magic angle twisted bilayer graphene. Of particular interest is the observed symmetry breaking between hole and electron doping that is characteristic of this type of superconductivity.
This topology drives the Fermi level away from the charge neutrality point, causing partially filled flat bands in magic-angle . This deformation also causes a charge redistribution in the twisted bilayer, causing a particular broken symmetry (central inset in
Figure 1) typically observed in high temperature superconductors and reported in magic-angle tBLG. Our findings also explain several exciting experimental observations in magic-angle tBLG, including striped charge order and evolution of the vibrational spectra, neither of which can be explained in terms of the conventional deformation mode with pure screw dislocations.
Our understanding of moiré physics deriving from dislocation concepts makes it possible to rationalize these and many other observed features within a well-established framework . Additional findings may yet emerge from this dislocation model for the moiré structure in tBLG. Indeed, while solitons provide one simple framework for understanding moiré patterns, there is no comparable concept of helical solitons…but helical dislocations have been observed in materials for more than seven decades!
Bistritzer R. and MacDonald A.H. Moiré bands in twisted double-layer graphene,
Cao Y et al. Unconventional superconductivity in magic-angle graphene superlattices,
Rakib T. Pochet P. Ertekin E. and Johnson H.T. Corrugation-driven symmetry breaking in magic-angle twisted bilayer graphene,
Communications Physics 2022
Rakib T., Pochet P., Ertekin E. & Johnson H.T. Helical dislocation in twisted bilayer graphene,
Ext. Mech. Letters 2023
 Pochet P. McGuigan B.C. Coraux J. and Johnson, H.T. Toward Moiré engineering in 2D materials via dislocation theory,
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