Carrier Scattering from Dynamical Magnetoconductivity in Quasineutral Epitaxial Graphene

Орлита, М.; Faugeras, C.; Grill, R.; Wysmołek, A.; Strupiński, Włodek; Berger, Claire; Heer, Walter A. de; Martinez, G.; Potemski, M.

doi:10.1103/physrevlett.107.216603

Cited by 66 publications

(92 citation statements)

References 40 publications

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“…By fitting the numerically calculated hot-carrier dynamics, we obtain the energy relaxation time of the photoexcited carriers, named the carrier scattering time. Figure 6b shows the calculated carrier scattering time t e ð Þ as a function of the excess carrier energy e for disorder-free undoped graphene ( e F j j¼ 0 meV) at a substrate temperature of 300 K. We observe that the carrier scattering time is precisely inverse to the carrier energy, t e ð Þ¼b= e j j (with bE0.9 eV ps), over a very broad energy range ( e j jB0.2-1.5 eV) in agreement with previous experimental studies on MEG 40 and graphite 41,42 . This behaviour is a direct consequence of the linear density of states and is therefore independent of the substrate temperature.…”

Section: Resultssupporting

confidence: 75%

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental carrier-carrier interactions and carrier-phonon relaxation processes in two-dimensional materials, and understanding of the physics underlying novel high-speed electronic and optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy and related techniques have interpreted the variety of observed signals within phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder. Here, we present an integrated experimental and theoretical programme, using ultrafast timeresolved terahertz spectroscopy combined with microscopic modelling, to systematically investigate the hot-carrier dynamics in a wide array of graphene samples having varying amounts of disorder and with either high or low doping levels. The theory reproduces the observed dynamics quantitatively without the need to invoke any fitting parameters, phenomenological models or extrinsic effects such as disorder. We demonstrate that the dynamics are dominated by the combined effect of efficient carrier-carrier scattering, which maintains a thermalized carrier distribution, and carrier-optical-phonon scattering, which removes energy from the carrier liquid.

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Section: Resultssupporting

confidence: 75%

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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“…A number of CR measurements have been performed on graphene, [22][23][24][25][26][27][28][29][30][31][32] successfully resolving the unusual LL structure, particularly when the graphene samples investigated have relatively high mobilities, such as exfoliated graphene or epitaxial graphene on SiC. However, for technologically important applications requiring large-area graphene films grown via chemical vapor deposition (CVD), we still face the current problem of low mobilities (∼10 3 cm 2 V −1 s −1 ), which severely broadens CR.…”

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confidence: 99%

Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields

et al. 2012

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Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples. The band structure of graphene exhibits a zero-gap linear dispersion relation near each of the Dirac points, which results in a variety of exotic properties of two-dimensional (2D) Dirac fermions. [1][2][3] While a number of electronic transport studies have revealed novel phenomena in the presence of a high magnetic field, including half-integer quantum Hall states observed at room temperature, 1,2,4 magneto-optical properties are expected to be equally unusual, 5-15 especially in the magnetic quantum limit 12 where the Fermi level resides in the lowest Landau level (LL). Even in conventional 2D electron systems such as found in GaAs quantum wells, studies of cyclotron resonance (CR) in the magnetic quantum limit have shown many-body effects, [16][17][18][19] such as spin splitting in the fractional quantum Hall regime, even though CR is not expected to be sensitive to electron-electron interactions due to Kohn's theorem. 20 The linear dispersions of graphene automatically evade this basic requirement for Kohn's theorem, motivating CR studies of graphene in ultrahigh magnetic fields.An applied magnetic field (B) creates LLs for charge carriers both in the conduction and valence bands, and CR measures resonant optical transitions between adjacent LLs ( n = ±1, where n is the Landau level index). 21 CR is a well-established and powerful technique to determine many fundamental parameters of a sample, such as carrier effective masses, densities, mobilities, and scattering rates. When performed with circularly polarized radiation, the sign of the charge carriers can also be determined. Furthermore, owing to graphene's nonparabolic (i.e., linear) dispersion, LL energies are not equally spaced; rather, they follow E n,± = ±c * √ 2ehBn, where n 0 and c * ≈ 1.0 × 10 6 m/s corresponds to the slope of the linear dispersions. Thus, different inter-Landau level (LL) transitions occur at different energies or magnetic fields. Hence, the absence or presence of a certain resonance can determine the Fermi energy. This is in marked contrast to conventional materials with parabolic dispersions, which form equally spaced LLs in a magnetic field [E n = (n + 1/2)ehB/m * , where m * is ...

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“…Since the LL energy is in turn proportional to √ B, this conclusion is consistent with direct measurements of LL widths as a function of B for MEG samples, where a √ B dependence is found for the LL widths. 7,8 Recent theoretical work analyzed different microscopic mechanisms of LL broadening and attributed this √ B dependence to an extrinsic mechanism involving scattering of the charge carriers by impurities.…”

Section: Discussionmentioning

confidence: 99%

“…Such information can be achieved by direct observations of the LLs by scanning tunneling spectroscopy, 3,4 infrared absorption, [5][6][7][8] and Raman scattering. [9][10][11] Alternatively, the broadening of LLs may be conveniently studied by an analysis of phonon Raman scattering, which is a versatile and widespread technique that probes structural and electronic properties of graphitic samples.…”

Section: Introductionmentioning

confidence: 99%

Damping of Landau levels in neutral graphene at low magnetic fields: A phonon Raman scattering study

et al. 2018

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Landau level broadening mechanisms in electrically neutral and quasineutral graphene were investigated through micro-magneto-Raman experiments in three different samples, namely, a natural single-layer graphene flake and a back-gated single-layer device, both deposited over Si/SiO2 substrates, and a multilayer epitaxial graphene employed as a reference sample. Interband Landau level transition widths were estimated through a quantitative analysis of the magnetophonon resonances associated with optically active Landau level transitions crossing the energy of the E2g Raman-active phonon. Contrary to multilayer graphene, the single-layer graphene samples show a strong damping of the low-field resonances, consistent with an additional broadening contribution of the Landau level energies arising from a random strain field. This extra contribution is properly quantified in terms of a pseudomagnetic field distribution ∆B = 1.0 − 1.7 T in our single-layer samples.

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Carrier Scattering from Dynamical Magnetoconductivity in Quasineutral Epitaxial Graphene

Cited by 66 publications

References 40 publications

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields

Damping of Landau levels in neutral graphene at low magnetic fields: A phonon Raman scattering study

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