Unique electronic states in biaxially heterostrained graphene bilayers moirés

Twist-moiré patterns have a demonstrated potential to allow engineering of bilayers of graphene to achieve many physical properties, by affecting the distribution of electrons and their interactions, as well as topological properties of the bands. One of the more novel approaches is to use heterostrain, the relative deformations between the layers, and the physical properties are particularly sensitive to that. We will show experimental evidence that heterostrain doesn't need the twist to express, but can induce new electronic states in aligned bilayers, through the formation of biaxial moirés. We will describe how the unique relaxation of these moirés form symmetry-breaking spiralling solitons that localize electronic states even more efficiently than twist moirés. This investigation is performed down to the atomic scale using Scanning Tunneling Microcopy and Spectroscopy. We also report detailed atomistic-relaxation and tight-binding calculations that include the exact stacking of the structure and permit to explain all the rich features of this moiré. Future works will surely benefit from including uniaxial and biaxial heterostrain to manipulate the electronic and topological states of graphene bilayers.