Mass-related inversion symmetry breaking and phonon self-energy renormalization in isotopically labeled AB-stacked bilayer graphene

Araujo, Paulo; Frank, Otakar; Mafra, D. L.; Fang, Wenjing; Kong, Jing; Dresselhaus, M. S.; Kalbáč, Martin

doi:10.1038/srep02061

Cited by 17 publications

(41 citation statements)

References 37 publications

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“…In addition, the ion gel dielectrics (PEO:LiClO 4 ) we used gives higher carrier densities (~3  10 ). 35,36,53 These differences may lead to distinct Raman features in our tBLG compared to those reported in recent literature. frequency is similar to that of the 2D band.…”

mentioning

confidence: 56%

“…35 Second, there are discontinuities in the gate dependent G frequencies, FWHMs, and integrated intensities when V TG~-1.5 V (~0.4 eV) (see Figs. 3ad).…”

Section: Textmentioning

confidence: 99%

“…The non-zero V D is ascribed to unintentional extrinsic doping from the Si substrate and the ion gel electrolyte. 32,35 The positive and negative signs of the (V TG -V D ) correspond to n-and p-doping in graphene, respectively. Doping dependence of the G and 2D bands from the SLG in our device is in good agreement with previous reports.…”

Section: Textmentioning

confidence: 99%

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Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric Doping

Chung¹,

Wu³

et al. 2015

Nano Lett.

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Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are studied using Raman spectroscopy in the twist angle regime where a resonantly enhanced G band can be observed. We observe prominent splitting and intensity quenching on the G Raman band when the carrier density is tuned away from charge neutrality. This G peak splitting is attributed to asymmetric charge doping in the two graphene layers, which reveals individual phonon selfenergy renormalization of the two weakly-coupled layers of graphene. We estimate the effective interlayer capacitance at low doping density of tBLG using an interlayer screening model. The anomalous intensity quenching of both G peaks is ascribed to the suppression of resonant 2 interband transitions between the two saddle points (van Hove singularities), that are displaced in the momentum space by gate-tuning. In addition, we observe a softening (hardening) of the R Raman band, a superlattice-induced phonon mode in tBLG, in electron (hole) doping. Our results demonstrate that gate modulation can be used to control the optoelectronic and vibrational properties in tBLG devices. TEXT:Recently there has been growing interest in two-dimensional (2D) van der Waals (vdW) materials and structures in which interlayer interaction can significantly affect these systems' properties and functionalities. [1][2][3][4][5][6][7][8][9] Twisted bilayer graphene (tBLG), in which the two graphene layers are stacked with a twist angle () and coupled by vdW force, has been demonstrated to show new physical (electronic, vibrational, and optical) properties through changed interlayer interaction at different twist angles. [10][11][12][13][14][15] Angle-resolved photoemission spectroscopy measurement has shown that tBLG exhibits weak interlayer coupling as revealed by the presence of van Hove singularities (VHSs) in the density of states at the overlap (saddle point) of two single layer graphene (SLG) Dirac cones. 13 Furthermore, low-energy, -dependent VHSs and superlattice Dirac cones have been observed by scanning tunneling microscopy and spectroscopy. [16][17][18] Optical spectroscopy has been exploited to study the optical and vibrational properties associated with the low-energy VHSs of tBLG. [19][20][21][22][23][24][25][26][27] These studies have demonstrated that tBLG is a prototype system to explore the influence of interlayer interaction in 2D layered materials. 3Raman spectroscopy is a sensitive probe of the unique electronic and phonon band structures of tBLG through resonance enhancement and superlattice induced Raman processes.Raman intensities from G and double-resonant (DR) ZO' L (fundamental layer-breathing vibration) bands display large resonance enhancements when the excitation photon energy equals to the inter-VHS energy (E VHS ; the energy difference between the saddle points in the conduction and valence bands). [19][20][21][22]27 The twist angle at which E VHS equals the excitation photon energy is called the critical angle  c . For 532 nm laser excitation, ...

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confidence: 56%

“…35 Second, there are discontinuities in the gate dependent G frequencies, FWHMs, and integrated intensities when V TG~-1.5 V (~0.4 eV) (see Figs. 3ad).…”

Section: Textmentioning

confidence: 99%

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Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric Doping

Chung¹,

Wu³

et al. 2015

Nano Lett.

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“…This problem can be promptly solved by isotope labeling of individual layers, as has been recently demonstrated [73][74][75]. One can easily tune the frequency of the phonons by an exchange of the 12 C isotope with a 13 C isotope with essentially no change to the electronic structure.…”

Section: Isotopesmentioning

confidence: 99%

“…In such a sample, we are able to address individual layers by Raman spectroscopy, follow the effect of phonon self-energy renormalizations for each individual layer separately and further understand how the interlayer (IL) interactions work in these isotopic systems. In the sample from Reference [75], a small central area is composed only from the 12 C isotope and the border area is composed of the 13 C isotope. The continuous layer that formed first is composed of the 12 C isotope [82].…”

Section: Isotopesmentioning

confidence: 99%

Intra- and Interlayer Electron-Phonon Interactions in 12/12C and 12/13C BiLayer Graphene

Mafra

Araújo

2014

Applied Sciences

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This review focuses on intra-and interlayer (IL) electron-phonon interactions and phonon self-energy renormalizations in twisted and AB-stacked bilayer graphene (2LG) composed either only of 12 C or a mixing of 12 C and 13 C isotopes. A simple way to imagine a 2LG is by placing one monolayer graphene (1LG) on top of another 1LG. The orientation of one of the layers with relation to the other may originate a twisted 2LG system (known as turbostratic) as well as a AB-stacked system, also known as Bernal stacking. By rotating the layers of a 2LG one can departure from a fully misoriented system to achieve the AB-stacked configuration and their IL interactions can be dramatically different being close to zero in a fully misoriented system and maximum in an AB-stacked system. Interlayer interactions are expected to slightly perturb the intralayer phonons and they also govern the low-energy electronic and vibrational properties, which are of primary importance to phenomena such as transport, infrared (IR) optics and telecommunication bands in the IR range. Therefore, a comprehensive discussion combining intra-and interlayer phenomena is necessary and addressed throughout the text.

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