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

## TL;DR

This paper demonstrates the formation of topological valley transport along a curved boundary in folded bilayer graphene, revealing long-range ballistic conduction through kink states in a high-quality domain wall.

## Contribution

It introduces a novel method to create a topological domain wall in folded bilayer graphene, enabling robust valley-polarized transport without complex fabrication.

## Key findings

- Measured resistance close to quantum resistance, indicating kink states.
- Observed long-range ballistic transport at the domain wall.
- Other regions exhibit tunable semiconducting behavior.

## Abstract

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 (1D) channel formed in bilayer graphene (BLG) under special electrostatic conditions or specific stacking configuration, called domain wall (DW). In these 1D channels, the valley-index defines the propagation direction of the charge carriers and the chiral edge states (kink states) are robust over many kinds of disorder. However, the fabrication of DWs is challenging, requiring the design of complex multi-gate structures or have been producing on rough substrates, showing a limited mean free path. Here, we report on a high-quality DW formed at the curved boundary of folded bilayer graphene (folded-BLG). At such 1D conducting channel we measured a two-terminal resistance close to the quantum resistance $R = e^2/4h$ at zero magnetic field, a signature of kink states. Our experiments reveal a long-range ballistic transport regime that occurs only at the DW of the folded-BLG, while the other regions behave like semiconductors with tunable band gap.