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Graphene-based QHE measurements

Graphene offers the possibility to greatly simplify the quantum Hall effect (QHE) standard used for electrical resistance calibrations - offering the same reference based on the von Klitzing constant (RK = h/e2) as at present, but allowing easier implementation at lower magnetic fields and higher temperatures. The sample fabrication technique that looks most promising for precision metrology applications uses graphene grown on SiC wafers, and there have been several advances over the last couple of years in this technique.

The BIPM was involved in some of the first precision measurements that demonstrated the equivalence between graphene and the existing GaAs references [1], and has now had the opportunity to study some samples that are close to delivering on the promise of simplified experimental conditions for routine use. In the framework of the GraphOhm EURAMET project, samples developed in a collaboration between MIKES-VTT and Aalto University (Finland) [2] were measured at the BIPM, and proved suitable for calibration use in the existing setup. An equivalence of a few parts in 109 was found with our traditional GaAs reference, although this was not yet possible with low field, high temperature and high measurement current simultaneously. Further sample improvements are expected in the near future and we envisage being able to implement a much simplified transportable system for on-site QHE comparisons (operating at 4 K temperature and 5 T field).

The collaboration (with both PTB and MIKES) also involved the investigation of a new generation of low frequency current comparators that could form the basis of room temperature resistance bridges to accompany the new graphene reference. The new comparators, built at MIKES, offer some improved characteristics over those presently used at the BIPM, and gave good results when substituted in our existing bridge electronics.

  1. Janssen, T.J.B.M. et al., 2011. Graphene, universality of the quantum Hall effect and redefinition of the SI system. New J. Phys., 13(9), p.093026.
  2. Novikov, S. et al., 2015. Fabrication and Study of Large-Area QHE Devices Based on Epitaxial Graphene., IEEE Trans. Instrum. Meas, 64(6), pp.1533-1538.
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