  Stacking two-dimensional layered materials such as graphene and transitional
metal dichalcogenides with nonzero interlayer twist angles has recently become
attractive because of the emergence of novel physical properties. Stacking of
one-dimensional nanomaterials offers the lateral stacking offset as an
additional parameter for modulating the resulting material properties. Here, we
report that the edge states of twisted bilayer zigzag graphene nanoribbons
(TBZGNRs) can be tuned with both the twist angle and the stacking offset.
Strong edge state variations in the stacking region are first revealed by
density functional theory (DFT) calculations. We construct and characterize
twisted bilayer zigzag graphene nanoribbon (TBZGNR) systems on a Au(111)
surface using scanning tunneling microscopy. A detailed analysis of three
prototypical orthogonal TBZGNR junctions exhibiting different stacking offsets
by means of scanning tunneling spectroscopy reveals emergent near-zero-energy
states. From a comparison with DFT calculations, we conclude that the emergent
edge states originate from the formation of flat bands whose energy and spin
degeneracy are highly tunable with the stacking offset. Our work highlights
fundamental differences between 2D and 1D twistronics and spurs further
investigation of twisted one-dimensional systems.
