Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2011-10-21
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
14 pages, 9 figures
Scientific paper
Metrological investigations of the quantum Hall effect (QHE) completed by transport measurements at low magnetic field are carried out in a-few-\mum-wide Hall bars made of monolayer (ML) or bilayer (BL) exfoliated graphene transferred on Si/SiO2 substrate. From the charge carrier density dependence of the conductivity and from the measurement of the weak localization quantum correction at low magnetic field, we deduce that transport properties in the devices are mainly governed by the Coulomb interaction of carriers with a large concentration of charged impurities. In the QHE regime, at high magnetic field and low temperature (T<1.3K), the Hall resistance is measured by comparison with a GaAs based quantum resistance standard using a cryogenic current comparator. In the low dissipation limit, it is found quantized within 5 parts in 10^7 (one standard deviation) at the expected rational fractions of the von Klitzing constant, respectively RK/2 and RK/4 in the ML and BL devices. These results constitute the most accurate QHE quantization tests in exfoliated graphene to date and the first in BL graphene. It turns out that a main limitation to the quantization accuracy, which is found well above the 10^-9 accuracy usually achieved in GaAs, is the low value of the QHE breakdown current being no more than 1 \muA. The current dependence of the longitudinal conductivity investigated in the BL Hall bar shows that dissipation occurs through quasi-elastic inter-Landau level scattering, assisted by large local electric fields. We propose that charged impurities are responsible for an enhancement of such inter-Landau level transition rate and cause small breakdown currents.
Glattli Christian D.
Guignard J.
Poirier W.
Schopfer Félicien
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