• DOI:10.1126/science.aax8201
• Corpus ID: 195798753

Helical quantum Hall phase in graphene on SrTiO3

@article{Veyrat2020HelicalQH,
  title={Helical quantum Hall phase in graphene on SrTiO3},
  author={Louis Veyrat and Corentin D{\'e}prez and Alexis Coissard and Xiaoxi Li and Fr{\'e}d{\'e}ric Gay and Kenji Watanabe and Takashi Taniguchi and Zheng Vitto Han and Benjamin A. Piot and Hermann Sellier and Benjamin Sac'ep'e},
  journal={Science},
  year={2020},
  volume={367},
  pages={781 - 786}
}

• L. Veyrat, Corentin Déprez, +8 authors B. Sac'ep'e
• Published 4 July 2019
• Physics
• Science

Controlling the interactions Near charge neutrality and subject to perpendicular magnetic fields, graphene is expected to become a ferromagnet with edge states not unlike those in two-dimensional topological insulators. Observing this effect experimentally has proven tricky because very large magnetic fields are needed to overcome the effect of electron-electron interactions, which drive the system to competing states. Instead of amping up the field, Veyrat et al. placed their graphene samples on a substrate made out of strontium titanate, which effectively screened the interactions. Transport measurements confirmed the formation of the characteristic edge states. Science, this issue p. 781 Transport measurements in graphene indicate edge states similar to those in 2D topological insulators. The ground state of charge-neutral graphene under perpendicular magnetic field was predicted to be a quantum Hall topological insulator with a ferromagnetic order and spin-filtered, helical edge channels. In most experiments, however, an insulating state is observed that is accounted for by lattice-scale interactions that promote a broken-symmetry state with gapped bulk and edge excitations. We tuned the ground state of the graphene zeroth Landau level to the topological phase through a suitable screening of the Coulomb interaction with the high dielectric constant of a strontium titanate (SrTiO3) substrate. Robust helical edge transport emerged at magnetic fields as low as 1 tesla and withstanding temperatures up to 110 kelvin over micron-long distances. This versatile graphene platform may find applications in spintronics and topological quantum computation.