Helical quantum Hall phase in screened graphene

Existence of a helical quantum Hall phase was evidenced recently in screened graphene placed in close proximity to SrTiO₃, a high dielectric constant substrate. However, the non-linear and hysteretic dielectric constant of SrTiO₃ make it a non-ideal candidate for reproducible high mobility devices. Here, we employ an atomically flat 2D metal placed a few nanometers away from the graphene plane to screen the Coulomb interactions. In resulting high mobility devices, we observe transport signatures of helical edge states present at very low fields. Furthermore, we present advanced device architectures involving a topgate to study the equilibration between the helical and chiral edge states. Our results are consistent with the helical edge transport picture.