Topological valley transport at the curved boundary of a folded bilayer graphene

The development of valleytronics demands long-range electronic transport with preserved valley index, a degree of freedom similar to electron spin. A promising structure for this end is a topological one-dimensional channel formed in a bilayer graphene, called a domain wall. In these channels, the valley-index defines the propagation direction of the charge carriers, and the chiral edge states are robust over many kinds of disorder. However, the fabrication of domain walls are challenging, requiring the design of complex multi-gate structures or production on rough substrates, showing a limited mean free path. Here, we report on a high-quality domain wall formed at the curved boundary of a folded bilayer graphene. Our experiments reveal long-range ballistic transport at such topological channels with the two-terminal resistance close to the ballistic resistance R = e2/4h at zero-magnetic field and the four-terminal resistance near to zero. At the bulk, we measure a tunable band gap.