Rotationally Controlled Atomic Layer Heterostructures*

Heterostructures of atomic layers such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides (TMDs) can serve as testbed for novel quantum phenomena in two-dimensions (2D). A key ingredient that can add a new dimension to the atomic layer heterostructures palette is the rotational control and alignment of different 2D layers. We review here an experimental technique that enables rotationally controlled heterostructures with accurate alignment of individual layer crystal axes [1]. We illustrate the applicability of this technique to the realization of tunable moiré patterns in twisted bilayer graphene [2], and rotationally aligned double layers of graphene [3], or TMDs [4] separated by a tunnel barrier, which display resonant, energy- and momentum-conserving tunneling in vertical transport. Rotationally aligned double bilayer graphene separated by a WSe₂ tunnel barrier, designed to study equilibrium indirect exciton formation, display a strongly enhanced tunneling at low temperatures when the two graphene bilayers are populated with carriers of opposite polarity and equal density [5]. The enhanced tunneling at overall neutrality departs markedly from single-particle model calculations, and suggests the emergence of a many-body state with when electrons and holes of equal densities populate the two layers.

Work done in collaboration with K. Kim, G. W. Burg, H. C. P. Movva, S. K. Banerjee, L. F, Register, A. H. MacDonald, T. Taniguchi, and K. Watanabe.

[1] K. Kim et al., Nano Lett. 16, 1989 (2016).
[2] K. Kim et al., Proc. Natl. Acad. Sci. USA 114, 3364 (2017).
[3] G. W. Burg et al., Nano Lett. 17, 3919 (2017).
[4] K. Kim et al., Nano Lett. 18, 5967 (2018).
[5] G. W. Burg et al., Phys. Rev. Lett. 120, 177702 (2018).