Local electronic signatures of impurity states in graphene

Wehling, T. O.; Balatsky, Alexander V.; Katsnelson, M. I.; Lichtenstein, A. I.; Scharnberg, K.; Wiesendanger, R.

doi:10.1103/physrevb.75.125425

Cited by 243 publications

(254 citation statements)

References 31 publications

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“…In combination with a finite bulk gap, this impurity induced cross-talk between surface and bulk causes the observed disruption of the Dirac spectrum by permitting second-order bulk-assisted scattering processes. In fact, the resonance states in a TI are similar to states found in both graphene [13][14][15] and d-wave high-temperature superconductors, 16 two other materials with Dirac-like lowenergy spectra, thus making a strong argument for a unified local response to impurities for all "Dirac" materials, 17 once any topological protection is lost.…”

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confidence: 72%

Strong potential impurities on the surface of a topological insulator

2012

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Topological insulators (TIs) are said to be stable against non-magnetic impurity scattering due to suppressed backscattering in the Dirac surface states. We solve a lattice model of a three-dimensional TI in the presence of strong potential impurities and find that both the Dirac point and low-energy states are significantly modified: low-energy impurity resonances are formed that produce a peak in the density of states near the Dirac point, which is destroyed and split into two nodes that move off-center. The impurity-induced states penetrate up to 10 layers into the bulk of the TI. These findings demonstrate the importance of bulk states for the stability of TIs and how they can destroy the topological protection of the surface.Comment: 4+ pages, 3 figures. Published versio

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confidence: 72%

Strong potential impurities on the surface of a topological insulator

2012

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“…As shown in the inset of Fig. 4(a), high-energy Landau levels oscillate remarkably in a magnetic field of strength B = 8 T, indicating that the Ag resonant impurities serve as mild disorder and do not broaden Landau levels seriously [6,8,17,33,57,60]. More interestingly, as B increases, the zeroth Landau level gradually starts to appear and play a dominant role; therefore, the central peak (a combination of resonant peak and the zeroth Landau-level peak) gradually moves away from the resonant peak measured under B = 0 T [see Fig.…”

Section: Resultsmentioning

confidence: 98%

“…3(a). The appearance of midgap states in disordered graphene's ADOS, although predicted by a large number of theoretical studies [5][6][7][8][9][10]17,21,25,42,57], has never been clearly demonstrated by other experimental methods. Quantum capacitance measurement of graphene devices can be used to study the overall effect of resonant impurities with different impurity concentrations n i on a large scale.…”

Section: Resultsmentioning

confidence: 99%

“…Theoretical predictions suggest that point defects and adsorbates in single-layer graphene induce midgap states near the Dirac point [5][6][7][8][9][10][11]. The local density of states (LDOS) in disordered graphene nanostructures has been investigated theoretically and experimentally [5][6][7][8][9][10][12][13][14][15][16][17]. Previous scanning tunneling spectroscopy studies have shown that robust LDOS peaks appear near a single vacancy in graphene or in hydrogenated graphene [12,13,16] These resonant impurities, however, have not been successfully detected in transport measurements because their transport behavior always mimics that of charged impurities at finite densities [9,10,[18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

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Detection of resonant impurities in graphene by quantum capacitance measurement

et al. 2014

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We investigated Ag-adatom-induced resonant impurities of graphene by quantum capacitance measurement. Different from charged impurities and other conventional resonant impurities, Ag atoms form very weak covalent bonds with graphene. The Ag-adatom-induced resonant peak as measured by quantum capacitance grows more intense at cryogenic temperatures, at higher impurity concentrations, and in stronger magnetic fields, in accordance with our theoretical calculations. The appearance of resonant states and the split of the zeroth Landau level for Ag-adsorbed graphene are manifestations of the formation of a flat impurity band near the Dirac point.

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“…Besides explaining the effect of single molecule detection reported in [13] it is capable of controlling the occupancy of flat impurity bands in graphene near the Dirac point and can give rise to exchange scattering. This earns future attention, as it can result in strongly spin-polarized impurity states [28] and guides a possible pathway [15] to high temperature magnetic order in this material.…”

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confidence: 99%

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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Local electronic signatures of impurity states in graphene

Cited by 243 publications

References 31 publications

Strong potential impurities on the surface of a topological insulator

Strong potential impurities on the surface of a topological insulator

Detection of resonant impurities in graphene by quantum capacitance measurement

Molecular Doping of Graphene

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