Abstract
At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking. If the interlayer bias is applied to open an energy gap inside the domain regions making them insulating, such marginally twisted bilayer graphene is expected to remain conductive due to a triangular network of chiral one-dimensional states hosted by domain boundaries. Here we study electron transport through this helical network and report giant Aharonov-Bohm oscillations that reach in amplitude up to 50% of resistivity and persist to temperatures above 100 K. At liquid helium temperatures, the network exhibits another kind of oscillations that appear as a function of carrier density and are accompanied by a sign-changing Hall effect. The latter are attributed to consecutive population of the narrow minibands formed by the network of one-dimensional states inside the gap.
Highlights
At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking
At the marginal twist angles, θ 1, the electronic structure is expected to become qualitatively different from that formed at magic or larger θ because the bilayer graphene (BLG) superlattice undergoes a strain-accompanied lattice reconstruction such that there appear large triangular domains with alternating Bernal (AB and BA) stacking order[11,12,13]
The domain regions are rather similar to the conventional BLG and, if the displacement field D is applied between the layers, a sizeable energy gap δ opens in the spectrum[11,19,20], making the domains insulating[19]
Summary
At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking. The domain regions are rather similar to the conventional BLG and, if the displacement field D is applied between the layers, a sizeable energy gap δ opens in the spectrum[11,19,20], making the domains insulating[19] Under these conditions, marginally twisted graphene (MTG) bilayers may still remain electrically conductive because walls between AB and BA domains allow one-dimensional (1D) chiral states[11,12,13,14,15,16,17,18,21–24] (Fig. 1a). Λ2, half the size of the superlattice unit cell that includes both AB and BA domains In this Communication, we study the electronic properties of MTG and report exceptionally strong Aharonov–Bohm oscillations[25] arising from electron interference along the triangular loops forming the chiral network. Our work shows that marginally twisted BLG is markedly distinct from other 2D electronic systems, including BLG at larger twist angles, and offers a fascinating venue for further research
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