Atomic defects in topological and correlated twisted van der Waals heterostructures

  Twisted van der Waals materials have risen as a powerful platform to engineer artificial quantum matter. Artificial moire heterostructures, in general, display two length scales, the original lattice constant and the emergent moire length. In particular, atomic defects in two-dimensional materials, including substitutional elements and vacancies, have a relevant length scale stemming from the microscopic lattice constant and, therefore, can give rise to a rich interplay with the moire length. Here we will address the impact of atomic defects in twisted graphene bilayers^[1,2], twisted graphene trilayers^[3], and artificial moire topological superconductors^[4]. First^[1,2], we show that local defects in twisted bilayer graphene allow realizing triple point fermions and that, in the presence of interactions, give rise to in-gap excitations in a superconducting moire state. Second^[3], by combining first-principles calculations and low-energy models, we show the impact of local impurities in the flat bands of twisted graphene trilayers and, in particular, the disruption of bulk valley currents. Third^[4], we demonstrate the critical dependence of the topological state on the interplay between atomic defects and the moire pattern in the moire topological superconductor NbSe₂/CrBr₃. These results highlight the key role of impurities in twisted van der Waals materials, revealing the key interplay between length and energy scales in artificial moire systems.

*Ref
 ^[1] Aline Ramires and Jose L. Lado, Phys. Rev. B 99, 245118 (2019)
 ^[2] Alejandro Lopez-Bezanilla and J. L. Lado, Phys. Rev. Materials 3, 084003 (2019)
 ^[3] Alejandro Lopez-Bezanilla and J. L. Lado, Phys. Rev. Research 2, 033357 (2020)
 ^[4] Maryam Khosravian and Jose L. Lado, Phys. Rev. Materials 6, 094010 (2022)