Selective Transmission and Backscattering of Helical Edge States in Screened Graphene Dual-Gated Devices

The ground state of charge-neutral graphene in the quantum Hall regime was predicted to be an insulating valley-polarized ferromagnet, arising from the enhancement of valley anisotropy terms due to long-range Coulomb interactions. By screening these interactions with a high-dielectric substrate, we induced a spin-polarized ferromagnetic phase that hosts spin-polarized helical edge states at the charge neutrality point (CNP). To investigate the transport characteristics of this helical edge phase, we designed dual-gated devices to locally modulate the carrier density in screened graphene. This configuration enabled selective transmission and backscattering of helical edge states through a tunable quantum Hall barrier. We present a model based on the Landauer-Büttiker formalism for helical edge states, which also accounts for the equilibration of these states with the chiral states in the local gate region. Our experimental results are consistent with this model.