Observation of Helical Edge States and Fractional Quantum Hall Effect in   a Graphene Electron-hole Bilayer
  A quantum Hall edge state provides a rich foundation to study electrons in 1-dimension (1d) but is limited to chiral propagation along a single direction. Here, we demonstrate a versatile platform to realize new 1d systems made by combining quantum Hall edge states of opposite chiralities in a graphene electron-hole bilayer. Using this approach, we engineer helical 1d edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong nonlocal transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Moreover, we investigate these electron-hole bilayers in the fractional quantum Hall regime, where we observe conduction through fractional and integer edge states of opposite chiralities, paving the way towards the realization of 1d helical systems with fractional quantum statistics. 
J. D. Sanchez-Yamagishi, J. Y. Luo, A. F. Young, B. Hunt, K. Watanabe,   T. Taniguchi, R. C. Ashoori, P. Jarillo-Herrero
cond-mat.mes-hall