Quantum Hall effect in graphene for resistance metrology
November 6, 2014 - 9:00am
The quantum Hall effect (QHE) observed in two dimensional electron gas at low temperature and under a strong perpendicular magnetic field has revolutionized the resistance metrology since its discovery in 1980 by Klaus von Klitzing. It provides a representation of the ohm based on the Planck constant and the electron charge only. In 2005, graphene, a purely two dimensional arrangement of carbon atoms in a honeycomb lattice, where the charge carriers behave as Dirac fermions, has revealed a new flavor of the QHE. From the metrological point of view the QHE in graphene is very promising since it is much more robust than in conventional semiconductors. It could lead to a more convenient resistance standard operating at higher temperature and lower magnetic induction, which is an advantage for a broader dissemination of a precise standard for industrial end-users.
During this presentation I’ll first present the impact in the QHE regime of line defects such as wrinkles or grain boundaries, ubiquitous in graphene grown by chemical vapor deposition on metal. We will show that these line defects lead to a non conventional dissipation mechanism that jeopardize the quantum Hall effect accuracy, pointing to the use of wrinkle-free monocrystals for further metrological studies.
The second part of my presentation will be focused on monolayer graphene grown by chemical vapor deposition on silicon carbide. We compared in detail the Hall resistance of the graphene sample from 10 T to 19 T at 1.4 K with a GaAs/AlGaAs resistance standard with a discrepancy of (-2± 4)x1010. For the first time a graphene-based standard was able to operate not only in the same temperature and magnetic field conditions as the semiconductor-based standard, but in a magnetic range more than ten times larger. We have carefully studied the dissipation mechanisms taking place in this sample and measured precisely the value of the localization length in the QHE regime. It saturates interestingly at the charge carrier wavelength, opening interesting questions about the close link between Hall quantization and localization physics in graphene grown on SiC.