1. What are the contributions in "Approaching ballistic transport in suspended graphene" ?
Here the authors show that the fluctuations are significantly reduced in suspended graphene samples and they report lowtemperature mobility approaching 200,000 cm V s for carrier densities below 5 3 10 cm.. The unusual low energy excitation spectrum of graphene, consisting of quasiparticles that are massless Dirac fermions, implies the emergence of novel electronic properties such as negative index of refraction, specular Andreev reflections at graphene–superconductor junctions8,9 and evanescent transport10.. Here the authors address one of the outstanding questions about graphene—what are its intrinsic transport properties close to the Dirac point—by studying graphene in the absence of a supporting substrate.. In a typical SG device ( Fig. 1b ), the graphene layer is suspended from the voltage leads, which run across the sample and at the same time provide structural support.. The particle–hole asymmetry seen in the figure is observed in all their samples, SG as well as NSG, if the lead separation is sufficiently short ( L, 1 mm ), but it becomes negligible in samples with large lead separation or in the samples with the Hall bar geometry.. The authors limit their discussion to the hole branch where well-defined Shubnikov-de-Haas ( ShdH ) oscillations are observed.. This suggests a slight permanent sagging of the SG devices that is attributed to the deformation of the leads by wicking action of liquids during the fabrication process.. Further studies are needed to determine the precise cause of the asymmetry.
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2. What is the density dependence of the mobility of the SG samples?
Because at low densities the mobility is mostly determined by long-range scattering15 (shortrange scattering is weak near the Dirac point due to the small density of states24), the lower mobility of the NSG samples implies that removal of the substrate eliminates the primary source of long-range scattering.
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3. What is the effect of the random potential on the SG?
The random potential introduces electron–hole puddles15–17 close to the Dirac point that cause spatial fluctuations in doping levels.
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4. What is the trend to positive slopes in the SG sample?
100 K, the trend to positive slopes suggests the onset of thermally induced long-range scattering, possibly due to thermally excited ripples18 or ripple-induced charge inhomogeneity28.
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