High-resolution tunnelling spectroscopy of a graphene quartet

Song, Young Jae; Otte, Alexander F.; Kuk, Young; Hu, Yusheng; Torrance, David; First, Phillip N.; Heer, Walt A. de; Min, Hongki; Adam, Shaffique; Stiles, Mark D.; MacDonald, Allan H.; Stroscio, Joseph A.

doi:10.1038/nature09330

Cited by 199 publications

(252 citation statements)

References 23 publications

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“…This is unlikely, also since g ≈ 2 was confirmed for epitaxial multilayer graphene on the C-face of SiC. 27 A change of D S can only be caused by the substrate as we expect the graphene to be comparable to eSLG 7 and growth related defects like grain boundaries do not show a strong effect on D S and τ S for CVD grown single layer graphene on SiO 2 . 6 One of the substrate related effects could be inhomogeneities of the graphene thickness and doping at terrace step edges 7 and scattering potentials resulting from that.…”

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confidence: 86%

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

et al. 2012

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We developed an easy, upscalable process to prepare lateral spin-valve devices on epitaxially grown monolayer graphene on SiC(0001) and perform nonlocal spin transport measurements. We observe the longest spin relaxation times τ S in monolayer graphene, while the spin diffusion coefficient D S is strongly reduced compared to typical results on exfoliated graphene.The increase of τ S is probably related to the changed substrate, while the cause for the small value of D S remains an open question.Spin transport in graphene draws great attention since the observation of spin relaxation lengths of λ S = 2 µm, with spin relaxation times in the order of τ S = 150 ps at room temperature (RT) in

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confidence: 86%

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

et al. 2012

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“…However, this splitting is hardly observable at higher energies. The AA-stacked trilayer graphene exhibits three groups of monolayer-like sequence of peaks [86,88,89] located at energies described by the simple relationship E c,v ∝ √ n c,v B, as indicated in Fig. 9(a).…”

Section: The Zero-field Band Structure and Quantized Landau Levelsmentioning

confidence: 99%

“…The exceptionally high peak at the Fermi level is a superposition of three peaks corresponding to the Dirac points; its intensity is proportional to the number of graphene layers. The essential differences of the DOS can be verifed by STS [86][87][88][89]; those profiles can then be used as a tool to identify the stacking configuration of graphene sheets.…”

Section: The Zero-field Band Structure and Quantized Landau Levelsmentioning

confidence: 99%

Configuration-enriched magneto-electronic spectra of AAB-stacked trilayer graphene

Lin

et al. 2015

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We developed the generalized tight-binding model to study the magneto-electronic properties of AAB-stacked trilayer graphene. Three groups of Landau levels (LLs) are characterized by the dominating subenvelope function on distinct sublattices. Each LL group could be further divided into two sub-groups in which the wavefunctions are, respectively, localized at 2/6 (5/6) and 4/6 (1/6) of the total length of the enlarged unit cell. The unoccupied conduction and the occupied valence LLs in each subgroup behave similarly. For the first group, there exist certain important differences between the two sub-groups, including the LL energy spacings, quantum numbers, spatial distributions of the LL wavefunctions, and the field-dependent energy spectra.The LL crossings and anticrossings occur frequently in each sub-group during the variation of field strengths, which thus leads to the very complex energy spectra and the seriously distorted wavefunctions. Also, the density of states (DOS) exhibits rich symmetric peak structures. The predicted results could be directly examined by experimental measurements. The magnetic quantization is quite different among the AAB-, AAA-, ABA-, and ABC-stacked configurations.

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“…The splitting of LL (0,+);(1,+) at E F is a sign of correlated electron behavior 28 . We examine this splitting in more detail in Fig.…”

mentioning

confidence: 99%

“…Accordingly, the interplay between the interactions, external and disorder-induced local electric fields, and localized states in the gap is becoming the central issue in the physics of the bilayer graphene system. Direct atomic-scale probing with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has been proven as a powerful technique [26][27][28] for studying this physics, particularly in revealing the effects of disorder on the graphene electronic states [29][30][31] .In this article, we present the first STM/STS measurements of a gated bilayer graphene device in magnetic fields ranging from zero to the quantum Hall regime. We investigate the local density of states and the formation of an energy band gap affected by disorder while tuning the total charge density, as the Fermi energy (E F ) is varied with an electrostatic back gate with respect to E D .…”

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confidence: 99%

Microscopic polarization in bilayer graphene

et al. 2011

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Bilayer graphene has drawn significant attention due to the opening of a band gap in its low energy electronic spectrum, which offers a promising route to electronic applications. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Our scanning tunneling measurements reveal the microscopic nature of the bilayer gap to be very different from what is observed in previous macroscopic measurements or expected from current theoretical models. The potential difference between the layers, which is proportional to charge imbalance and determines the gap value, shows strong dependence on the disorder potential, varying spatially in both magnitude and sign on a microscopic level. Furthermore, the gap does not vanish at small charge densities. Additional interaction-induced effects are observed in a magnetic field with the opening of a subgap when the zero orbital Landau level is placed at the Fermi energy.Bilayer graphene consists of two graphene sheets overlaid in the Bernal stacking orientation where A 2 atoms of the top layer lie on top of the B 1 atoms of the bottom layer (see * These authors contributed equally to this work.§ To whom correspondence should be addressed: nikolai.zhitenev@nist.gov, joseph.stroscio@nist.gov.2 Fig. 1a), connected by the interlayer coupling 1 γ , thus breaking the A/B sublattice symmetry in the individual graphene layers. This results in massive chiral fermions where the electronic energy dispersion is hyperbolic in momentum, in contrast to the linear dispersion that leads to massless carriers in single layer graphene 1,2 . In bilayer graphene the energy bands still meet at the charge neutrality point (E D ) in the absence of an electric field between the layers (neglecting interaction effects) (Fig. 1b). In an applied electric field a potential asymmetry is developed between the layers, resulting in the opening of an energy band gap between the low lying bands making bilayer graphene of intense interest in electronic applications ( Fig. 1b) [2][3][4][5][6][7][8][9][10] . Bilayer graphene also differs from single layer graphene in its magnetic quantization in the quantum Hall regime. At E D , the four-fold degenerate Landau level (LL) in single layer graphene becomes eight-fold degenerate in the bilayer due to the additional layer degeneracy 3,11,12 . When the gap is opened this manifold splits into two four-fold degenerate quartets polarized on each layer at low energies. Lifting of these degeneracies have been observed in recent measurements [13][14][15][16] .Theoretical studies 17,18 suggest the existence of interaction-driven band gaps, which are even possible in zero applied field with corresponding quantum Hall ferromagnetic states 17,19 .The energy band gap in bilayer graphene has been studied by optical measurements such as angle resolved photoemission spectroscopy 20 and infrared spectroscopy [4][5][6]21 , which demonstrate that the gap is externally tunable and can reach values up to ≈ 250 meV...

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High-resolution tunnelling spectroscopy of a graphene quartet

Cited by 199 publications

References 23 publications

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)

Configuration-enriched magneto-electronic spectra of AAB-stacked trilayer graphene

Microscopic polarization in bilayer graphene

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