  The electronic properties of graphene superlattices have attracted intense
interest that was further stimulated by the recent observation of novel
many-body states at "magic" angles in twisted bilayer graphene (BLG). For very
small ("marginal") twist angles of 0.1 deg, BLG has been shown to exhibit a
strain-accompanied reconstruction that results in submicron-size triangular
domains with the Bernal stacking. If the interlayer bias is applied to open an
energy gap inside the domain regions making them insulating, marginally-twisted
BLG is predicted to remain conductive due to a triangular network of chiral
one-dimensional (1D) states hosted by domain boundaries. Here we study electron
transport through this network and report giant Aharonov-Bohm oscillations
persisting to temperatures above 100 K. At liquid helium temperatures, the
network resistivity 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 flat minibands
formed by the 2D network of 1D states inside the gap. 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.
