Low <i>B</i> Field Magneto-Phonon Resonances in Single-Layer and Bilayer Graphene

Neumann, Christoph; Reichardt, Sven; Drögeler, Marc; Terrés, Bernat; Watanabe, Kenji; Beschoten, Bernd; Rotkin, Slava V.; Stampfer, Christoph

doi:10.1021/nl5038825

Cited by 33 publications

(73 citation statements)

References 42 publications

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“…We therefore conclude that the electron mobility in our sample is limited by intra-valley scattering events that are most likely caused by local strain fluctuations. This conclusion agrees with evidence we have from Raman experiments that high-mobility samples exhibit reduced strain fluctuations [42], as well as with recent studies on single-layer graphene, which also identified mechanical deformations as the main source of limiting mobility [43]. This in turn strongly suggests that the transport properties of both single-and bilayer graphene are hindered by the same physical mechanism.…”

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confidence: 92%

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

et al. 2014

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We present transport measurements on high-mobility bilayer graphene fully encapsulated in hexagonal boron nitride. We show two terminal quantum Hall effect measurements which exhibit full symmetry broken Landau levels at low magnetic fields. From weak localization measurements, we extract gate-tunable phase coherence times τ φ as well as the inter-and intra-valley scattering times τi and τ * . While τ φ is in qualitative agreement with an electron-electron interaction mediated dephasing mechanism, electron spin-flip scattering processes are limiting τ φ at low temperatures. The analysis of τi and τ * points to local strain fluctuation as the most probable mechanism for limiting the mobility in high-quality bilayer graphene.PACS numbers: 72.15.Rn, 73.43.Qt Bilayer graphene (BLG) is an interesting material system to explore phase-coherent mesoscopic transport with unique electronic properties [1]. In contrast to singlelayer graphene, in BLG a band gap can be opened by an external electric field [2,3] making local depletion of the two-dimensional electron gas (2DEG) possible similar to III/V heterostructures. This is an important prerequisite for implementing state-of-the-art phase-coherent quantum device concepts [4,5]. In contrast to conventional 2DEGs, the massive Dirac fermion nature of the quasiparticles in BLG results in an unconventional quantum Hall effect [6,7] and promises unique quantum interference properties [8]. So far, the observable transport phenomena in BLG devices suffer from the limited device quality which is most likely a consequence of the high sensitivity of BLG on the surrounding environment. Recent developments in device fabrication have shown that a significant improvement in sample quality can be obtained by replacing conventional SiO 2 with hexagonal boron nitride (hBN) [9]. This material provides an ultraflat substrate for graphene [9,10] and enables the realization of the high-mobility samples that are required to study, e.g. quantum phase transitions in the lowest quantum Hall state [11] or superlattice effects such as the Hofstadter butterfly [12][13][14]. However, despite these improvements, it remains difficult to experimentally address the microscopic mechanisms that limits carrier mobility and phase-coherence in high-quality BLG. To address these important questions, we present diffusive transport measurements on BLG fully encapsulated in hBN. Our fabrication technique allows to obtain highmobility samples, which show a well-developed quantum Hall effect and a full degeneracy breaking of the zero Landau level around B = 6 T. To investigate the limits of phase-coherent transport and to gain insights on the limitations to carrier mobility in these devices, we perform weak localization measurements [15]. From these measurements, we extract the inter-and intra-valley scattering times, as well as the phase-coherence time. Our results indicate (i) that the main sources of dephasing in high-quality BLG are the electron-electron interaction as well as electron spin-flip scattering, ...

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confidence: 92%

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

et al. 2014

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“…[5][6][7] In particular, material stacks built around graphene (Gr) promise interesting electronic properties [8][9][10][11][12] and many possibilities for hosting high-quality devices. Different two-dimensional materials have been shown to be favorable substrates for graphene in such stacks.…”

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confidence: 99%

“…In particular, the small full width at half maximum (FWHM) of the graphene 2D line of around 17 cm −1 is an indication of the high crystal quality and local flatness of the encapsulated graphene sheet. 12,22 A scanning force microscopy (SFM) image of the Hall bar is shown in Figure 1e. Comparison with a scanning Raman microscopy image (Figure 1f), showing the intensity of the prominent Si Raman line at 520 cm −1 (see spectra in Figure 1d), reveals the high spatial resolution of our optical setup.…”

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confidence: 99%

Spatial Control of Laser-Induced Doping Profiles in Graphene on Hexagonal Boron Nitride

Neumann

Rizzi

Reichardt

et al. 2016

ACS Appl. Mater. Interfaces

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We present a method to create and erase spatially resolved doping profiles in graphenehexagonal boron nitride (hBN) heterostructures. The technique is based on photo-induced doping by a focused laser and does neither require masks nor photo resists. This makes our technique interesting for rapid prototyping of unconventional electronic device schemes, where the spatial resolution of the rewritable, long-term stable doping profiles is only limited by the

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“…In order to exclude other effects, the pseudomagnetic field must be uniform within the laser spot size in the confocal Raman spectroscopy experiment, which is exactly what we showed and discussed in this paper. By following the recent experiment of Neumann et al [21], where MPRs at low magnetic fields have been observed, we can estimate the experimental requirements for observing MPR shifts thanks to a tunable pseudomagnetic field. The most prominant MPR below 20 T is the so-called T 1 transistion at around 3.7 T, which results in an well resolved peak of the Raman G-line width as function of magnetic field.…”

Section: Experimental Implicationsmentioning

confidence: 99%

“…Therefore, strained graphene offers the unique opportunity to study the electronic properties of graphene at extreme (pseudo)magnetic field strengths. Alternatively, such systems could allow studies to the magneto-phonon resonance in Raman spectroscopy [21] or enable so-called valley-tronics [22][23][24]. Numerical work of strain fields in graphene is therefore of additional value, as it not only estimates the strength of the pseudomagnetic field, but also shows the uniformity of the generated pseudomagnetic field and its dependence on the lattice orientation with respect to the strain direction.…”

Section: Introductionmentioning

confidence: 99%

Uniformity of the pseudomagnetic field in strained graphene

2015

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We present a study on the uniformity of the pseudomagnetic field in graphene as a function of the relative orientation between the graphene lattice and straining directions. For this, we strained a regular micron-sized graphene hexagon by deforming it symmetrically by displacing three of its edges. By simulations, we found that the pseudomagnetic field is strongest if the strain is applied perpendicular to the armchair direction of graphene. For a hexagon with a side length of 1 µm, the pseudomagnetic field has a maximum of 1.2 T for an applied strain of 3.5% and it is uniform (variance < 1%) within a circle with a diameter of ∼ 520 nm. This diameter is on the order of the typical diameter of the laser spot in a state-of-the-art confocal Raman spectroscopy setup, which suggests that observing the pseudomagnetic field in measurements of shifted magneto-phonon resonance is feasible.

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Low B Field Magneto-Phonon Resonances in Single-Layer and Bilayer Graphene

Cited by 33 publications

References 42 publications

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene

Spatial Control of Laser-Induced Doping Profiles in Graphene on Hexagonal Boron Nitride

Uniformity of the pseudomagnetic field in strained graphene

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