Graphene p-n junction Arrays as Quantum-Hall Resistance Standards
  We demonstrate a device concept to fabricate resistance standards made of quantum Hall series arrays by using p-type and n-type graphene. The ambipolar nature of graphene allows fabricating series quantum Hall resistors without complex multi-layer metal interconnect technology, which is required when using conventional GaAs two-dimensional electron systems. As a prerequisite for a precise resistance standard we confirm the vanishing of longitudinal resistance across a p-n junction for metrological relevant current levels in the range of a few \muA. 
Miros{\l}aw Woszczyna, Miriam Friedemann, Thorsten Dziomba, Thomas   Weimann, and Franz J. Ahlers
cond-mat.mes-hall