Approaching ballistic transport in suspended graphene

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Abstract

The discovery of graphene1,2 raises the prospect of a new class of nanoelectronic devices based on the extraordinary physical properties3,4,5,6 of this one-atom-thick layer of carbon. Unlike two-dimensional electron layers in semiconductors, where the charge carriers become immobile at low densities, the carrier mobility in graphene can remain high, even when their density vanishes at the Dirac point. However, when the graphene sample is supported on an insulating substrate, potential fluctuations induce charge puddles that obscure the Dirac point physics. Here we show that the fluctuations are significantly reduced in suspended graphene samples and we report low-temperature mobility approaching 200,000 cm2 V−1 s−1 for carrier densities below 5 × 109 cm−2. Such values cannot be attained in semiconductors or non-suspended graphene. Moreover, unlike graphene samples supported by a substrate, the conductivity of suspended graphene at the Dirac point is strongly dependent on temperature and approaches ballistic values at liquid helium temperatures. At higher temperatures, above 100 K, we observe the onset of thermally induced long-range scattering.

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Figure 1: Suspended graphene (SG) sample characterization.
Figure 2: Carrier density dependence of transport.
Figure 3: Potential fluctuations.
Figure 4: Mobility and mean free path (mfp) of hole branch carriers.

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Acknowledgements

We thank G. Li and Z. Chen for discussions, S.W. Cheong and M. Gershenson for use of the atomic force microscope and e-beam equipment, V. Kiryukhin for the highly ordered pyrolytic graphite crystals, F. Guinea, A.H. Castro Neto, A. Balatsky, M. Fogler and D. Abanin for further useful discussions. Our work was supported by DOE DE-FG02-99ER45742; and ICAM.

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Correspondence to Eva Y. Andrei.

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