Abnormal conductivity in low-angle twisted bilayer graphene

Abstract

Controlling the interlayer twist angle offers a powerful means for tuning the electronic properties of two-dimensional (2D) van der Waals materials. Typically, the electrical conductivity would increase monotonically with decreasing twist angle owing to the enhanced coupling between adjacent layers. Here, we report a nonmonotonic angle-dependent vertical conductivity across the interface of bilayer graphene with low twist angles. More specifically, the vertical conductivity enhances gradually with decreasing twist angle up to a crossover angle at θc ≈ 5°, and then it drops notably upon further decrease in the twist angle. Revealed by density functional theory calculations and scanning tunneling microscopy, the abnormal behavior is attributed to the unusual reduction in average carrier density originating from local atomic reconstruction. The impact of atomic reconstruction on vertical conductivity is unique for low-angle twisted 2D van der Waals materials and provides a strategy for designing and optimizing their electronic performance.

Electronic properties of twisted multilayer graphene

“…The atomic structure was optimized until all force components are smaller than 0.5 meV/atom and the electronic calculations were then performed. The atomic structure relax- ation obtained by this method is shown to be in good agreement with experiments [18,[65][66][67] as well as the results obtained by other (both quantum and semi-classical) methods [60,[68][69][70], except that the intralayer equilibrium C-C bond distance is slightly overestimated by ∼ 1% [64].…”

Interlayer exciton formation, relaxation, and transport in TMD van der Waals heterostructures

“…However, note that when the twist angle between layers was rather small (generally less than 1°), atomic reconstruction could take place and was expected to have a profound effect on the band structures of the twisted bilayers 190 – 193 . In this case, the continuously varying rigid-lattice moiré pattern transformed to discrete commensurate domains divided by narrow domain walls, which had also been recently observed in twisted TMD vdW bilayers 194 , 195 .…”

“…All these works indicate that the diffusion barrier introduced by the moiré potential could be modified to affect exciton migration by tuning the twist angle or stacking mode between the constituent monolayers, which offers a novel way to control the exciton transport behavior in potential excitonic devices. However, note that when the twist angle between layers was rather small (generally less than 1°), atomic reconstruction could take place and was expected to have a profound effect on the band structures of the twisted bilayers [190][191][192][193] . In this case, the continuously varying rigidlattice moiré pattern transformed to discrete commensurate domains divided by narrow domain walls, which had also been recently observed in twisted TMD vdW bilayers 194,195 .…”

Robustness of structural superlubricity beyond rigid models

“…This effect was reported for twisted bilayer graphene at "magic" stacking angles (    1 1 ), demonstrating intrinsic unconventional superconductivity, as well as renormalized vibrational and electronic structures [44,45]. Recent studies identified local atomic reconstruction up to a crossover angle of rigid twist at 5°, which results in abnormal electrical conductivity [46]. Our simulation results for a bilayer with     0 7 show that the moiré pattern selforganizes into a reconstructed triangular network by sacrificing the elastic deformation in graphene layers.…”