Graphene, universality of the quantum Hall effect and redefinition of the SI system

The Système Internationale d’unités (SI) is about to undergo its biggest change in half a century by redefining the units for mass and current in terms of the fundamental constants h and e, respectively. This change crucially relies on the exactness of the relationships that link these constants to measurable quantities. Here we report the first direct comparison of the integer quantum Hall effect (QHE) in epitaxial graphene with that in GaAs/AlGaAs heterostructures. We find no difference in the quantized resistance value within the relative standard uncertainty of our measurement of 8.6× 10−11, this being the most stringent test of the universality of the QHE in terms of material independence. The new quantum Système Internationale d’unités (SI) units for mass and current will be based on the fundamental constants of nature: Planck’s constant, h, and the electron charge, e. Confidence in the new definition relies mainly on the ability to confirm experimentally the exactness of the relationships that link these constants to measurable quantities. The quantum Hall effect (QHE) defines one such relationship through the theoretical argument that the Hall resistance is quantized in units of h/Ne, where N is an integer. The QHE 6 Author to whom any correspondence should be addressed. New Journal of Physics 13 (2011) 093026 1367-2630/11/093026+06$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft