Sub-Poissonian Shot Noise in Graphene

Tworzydło, J.; Trauzettel, Björn; Titov, M.; Rycerz, Adam; Beenakker, C. W. J.

doi:10.1103/physrevlett.96.246802

Cited by 869 publications

(1,150 citation statements)

References 17 publications

(23 reference statements)

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“…novel electronic properties such as negative index of refraction 6 , specular Andreev reflections at graphene-superconductor junctions 7,8 , evanescent transport 9 , anomalous phonon softening 10 , etc. A basic assumption behind these intriguing predictions is that the graphene layer is minimally affected by interactions with the environment.…”

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confidence: 99%

Approaching ballistic transport in suspended graphene

et al. 2008

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The recent discovery of methods to isolate graphene 1-3 , a one-atom-thick layer of crystalline carbon, has raised the possibility of a new class of nano-electronics devices based on the extraordinary electrical transport and unusual physical properties 4,5 of this material. However, the experimental realization of devices displaying these properties was, until now, hampered by the influence of the ambient environment, primarily the substrate. Here we report on the fabrication of Suspended Graphene (SG) devices and on studies of their electrical transport properties. In these devices, environmental disturbances were minimized allowing unprecedented access to the intrinsic properties of graphene close to the Dirac Point (DP) where the energy dispersion of the carriers and their density-of-states vanish linearly giving rise to a range of exotic physical properties. We show that charge inhomogeneity is reduced by almost one order of magnitude compared to that in Non-Suspended Graphene (NSG) devices. Moreover, near the DP, the mobility exceeds 100,000 cm 2 /Vs, approaching theoretical predictions for evanescent transport in the ballistic model. The low energy excitation spectrum of graphene mimics relativistic particles -massless Dirac fermions (DF) -with an electron-hole symmetric conical energy dispersion and .vanishing density of states at the DP. Such unusual spectrum is expected to produce 1 novel electronic properties such as negative index of refraction 6 , specular Andreev reflections at graphene-superconductor junctions 7,8 , evanescent transport 9 , anomalous phonon softening 10 , etc. A basic assumption behind these intriguing predictions is that the graphene layer is minimally affected by interactions with the environment. However in reality the environment 11,12 and in particular the substrate 13 , can be quite invasive for such ultra-thin films. For example, the carrier mobility in graphene deposited on a substrate such as Si/SiO 2 deteriorates due to trapped charges in the oxide or to contaminants that get trapped at the graphene-substrate interface during fabrication. The substrate-induced charge inhomogeneity is particularly deleterious near the DP where screening is weak, 14,15 leading to reduced carrier mobility there. In addition, the atomic roughness of the substrate introduces short range scattering centers and may contribute to quench-condensation of ripples within the graphene layer 16 .In order to eliminate substrate induced perturbations, graphene films were suspended from Au/Ti contacts to bridge over a trench in a SiO 2 substrate. In contrast to prior realizations of suspended graphene 17,18 which did not provide electrical contacts for transport measurements, the SG devices described here incorporate multiple electrodes that allow 4-lead transport measurements. The SG devices employed here were fabricated from conventional NSG devices using wet chemical etching (see supporting online material). In a typical SG device, shown in Figure 1b, the graphene layer is suspended from the voltage l...

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Approaching ballistic transport in suspended graphene

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Molecular Doping of Graphene

et al. 2007

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Graphene, a one-atom thick zero gap semiconductor [1,2], has been attracting an increasing interest due to its remarkable physical properties ranging from an electron spectrum resembling relativistic dynamics [3,4,5,6,7,8,9,10,11,12] to ballistic transport under ambient conditions [1,2,3,4]. The latter makes graphene a promising material for future electronics and the recently demonstrated possibility of chemical doping without significant change in mobility has improved graphene's prospects further [13]. However, to find optimal dopants and, more generally, to progress towards graphene-based electronics requires understanding the physical mechanism behind the chemical doping, which has been lacking so far. Here, we present the first joint experimental and theoretical investigation of adsorbates on graphene. We elucidate a general relation between the doping strength and whether or not adsorbates have a magnetic moment: The paramagnetic single NO 2 molecule is found to be a strong acceptor, whereas its diamagnetic dimer N 2 O 4 causes only weak doping. This effect is related to the peculiar density of states of graphene, which provides an ideal situation for model studies of doping effects in semiconductors. Furthermore, we explain recent results on its "chemical sensor" properties, in particular, the possibility to detect a single NO 2 molecule [13].Controlling the type and the concentration of charge carriers is at the heart of modern electronics: It is the ability of combining gate voltages and impurities for locally changing the density of electrons or holes that allows for the variety of nowadays available semiconductor based devices. However, the conventional Si-based electronics is expected to encounter fundamental limitations at the spatial scale below 10 nm, according to the semiconductor industry roadmap, and this calls for novel materials that might substitute or complement Si. Being only one atomic layer thick, graphene exhibits ballistic transport on a submicron scale and can be doped heavily -either by gate voltages or molecular adsorbateswithout significant loss of mobility [1]. In addition, later experiments [13] demonstrated its potential for solid state gas sensors and even the possibility of single molecule detection.We show, that in graphene, aside from the donoracceptor distinction, there are in general two different classes of dopants -paramagnetic and nonmagnetic. In contrast to ordinary semiconductors, the latter type of impurities act generally as rather weak dopants, whereas the paramagnetic impurities cause strong doping: Due to the linearly vanishing, electron-hole symmetric density of states (DOS) near the Dirac point of graphene, localised impurity states without spin polarisation are pinned to the centre of the pseudogap. Thus impurity states in graphene distinguish strongly from their counterparts in usual semiconductors, where the DOS in the valence and conduction bands are very different and impurity levels lie generally far away from the middle of the gap. Impurity effects on t...

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“…Using a cryogenic, lownoise amplification set-up, we measure shot noise as a function of the gate voltage in two-terminal field-effect graphene devices. The results are successfully compared with the theoretical values derived by solving the Dirac equation [2,3]. Even though the shot noise at the Dirac point is equivalent to that of a regular diffusive conductor, clear distinction in the noise behavior can be found in the gate dependence.…”

Section: Introductionmentioning

confidence: 49%

“…It has been theoretically shown that in perfect graphene at the Dirac point, the conduction occurs only via evanescent waves, i.e. via tunneling between the leads [2,3]. This has interesting consequences on the conductivity and on the shot noise, both of which display universal behavior in the limit of wideaspect-ratio sheets.…”

Section: Introductionmentioning

confidence: 99%

Shot noise measurements in graphene

Danneau

Craciun

et al. 2009

Solid State Communications

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a b s t r a c tWe have investigated shot noise at microwave frequencies in wide-aspect-ratio graphene sheets in the temperature range of 4.2-30 K. We find that for our short (L < 300 nm) graphene samples with width over length ratio W /L > 3, the Fano factor F reaches a maximum F ∼ 1/3 at the Dirac point and that it decreases substantially with increasing charge density. Our results agree with the theoretical prediction that electrical transport at the Dirac point is governed by evanescent electronic states.

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Sub-Poissonian Shot Noise in Graphene

Cited by 869 publications

References 17 publications

Approaching ballistic transport in suspended graphene

Approaching ballistic transport in suspended graphene

Molecular Doping of Graphene

Shot noise measurements in graphene

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