Carrier multiplication in graphene under Landau quantization

Wendler, Florian; Knorr, Andreas; Malić, Ermin

doi:10.1038/ncomms4703

Cited by 64 publications

(102 citation statements)

References 37 publications

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“…The latter leads to an increase of the carrier density and is responsible for the appearance of CM. In previous studies, a significant carrier multiplication has been predicted in optically excited graphene [2][3][4] as well as Landau-quantized graphene [5]. Meanwhile carrier multiplication has also been demonstrated in time-dependent ARPES measurements [6] as well as in high-resolution pumpprobe studies [7][8][9].…”

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confidence: 82%

Experimentally accessible signatures of Auger scattering in graphene

2016

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The gapless and linear electronic band structure of graphene opens up Auger scattering channels bridging the valence and the conduction band and changing the charge carrier density. Here, we reveal experimentally accessible signatures of Auger scattering in optically excited graphene. To be able to focus on signatures of Auger scattering, we apply a low excitation energy, weak pump fluences, and a cryostatic temperature, so that all relevant processes lie energetically below the optical phonon threshold. In this regime, carrier-phonon scattering is strongly suppressed and Coulomb processes govern the carrier dynamics. Depending on the excitation regime, we find an accumulation or depletion of the carrier occupation close to the Dirac point. This reflects well the behavior predicted from Auger-dominated carrier dynamics. Based on this observation, we propose a multicolor pump-probe experiment to uncover the extreme importance of Auger channels for the nonequilibrium dynamics in graphene.

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confidence: 82%

Experimentally accessible signatures of Auger scattering in graphene

2016

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“…Here, we neglect the impact of carrier-carrier interaction on the LL dynamics since the occupations of only a small number of Landau levels around the Fermi energy are changed by low-energy terahertz radiation. Consequently, the energy-conserving carrier-carrier scattering channels are strongly suppressed by Pauli blocking [9,21]. We have verified the validity of this approximation by performing calculations with and without taking into account the Coulomb interaction in different regimes.…”

Section: A Semiconductor Bloch Equationsmentioning

confidence: 57%

“…The nonequidistant Landau-level spectrum and the optical selection rules of Landau-quantized graphene allow the excitation of specific inter-LL transitions using circularly polarized light. As a result, one can track the path of excited electrons towards a thermalized Fermi distribution [5][6][7][8][9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…The applied microscopic approach is based on the density matrix formalism, a wellestablished method for modeling the many-particle-induced carrier dynamics in graphene with and without the influence of a magnetic field [9,15,[17][18][19]. In accordance with a recent pump-probe experiment [14], we consider terahertz photons with an energy of 14 meV which is well below the cyclotron energy ω c 36 meV √ B at magnetic field strengths of B = 1 T. In conventional semiconductors with an equidistant Landau quantization, the absorption of low-energy terahertz photons is generally strongly suppressed, unless the cyclotron energy coincides with the photon energy.…”

Section: Introductionmentioning

confidence: 99%

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Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Wendler

Malić

2016

Phys. Rev. B

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We investigate the intraband carrier dynamics in Landau-quantized graphene after an optical excitation with low-energetic terahertz pulses. Based on a microscopic theory, we calculate time-dependent differential transmission spectra reflecting the Landau-level dynamics. Our calculations reveal a strong dependence on the Fermi energy E F of the graphene sample as well as on the applied magnetic field B. We find that the pump pulse can lead to both absorption bleaching and absorption enhancement depending on B and the position of E F with respect to the resonant Landau-level transition. As a result, positive and negative contributions in differential transmission spectra appear, in good agreement with recent pump-probe measurements.

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“…A signi cant carrier multiplication has been theoretically predicted [30,130,134] and experimentally con rmed in graphene [32,101,128,133,135]. So far, the theoretical studies have been constrained to the case of undoped graphene.…”

Section: Carrier Multiplication In Doped Graphenementioning

confidence: 97%

Relaxation Dynamics in Graphene

Malić

Knorr

2013

Graphene and Carbon Nanotubes

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In this thesis, the relaxation dynamics of nonequilibrium carriers in graphene is investigated. Based on the density matrix approach, the interaction of carriers with light, phonons and electrons is theoretically modelled. The resulting time-, momentum-, and angle-resolved simulation of the carrier dynamics enables the interpretation of recent experimental observations. Typically, the carrier relaxation has been accessed via high-resolution pump-probe experiments. Common to all studies is a bi-exponential decay of the pump-induced differential transmission (DT) spectrum. The fast decay component in the range of few tens of femtoseconds is assigned to an ultrafast Coulomb-dominated carrier redistribution towards a hot Fermi-Dirac distribution, whereas the slower decay component in the range of a picosecond reflects the equilibration between the electron and the phonon system. However, many studies report a zero-crossing after the initial decay in the transient DT spectrum, where the second decay component characterizes the recovering of the DT signal. In very good agreement with recent pump-probe experiment performed by the group of Prof. Manfred Helm (Helmholtz-Zentrum Dresden-Rossendorf), a microscopic explanation for the occurrence of transient negative differential transmission in graphene is found, where a detailed interplay of intraand interband absorption processes on the transient DT in graphene is investigated. In particular, phonon-assisted intraband processes are shown to lead to an enhanced absorption giving rise to the experimentally observed zero-crossing from positive to negative DT signals.In collaboration with the group of Prof. Theodore B. Norris (Michigan University, USA), theoretical studies combined with ultrafast time-resolved THz spectroscopy were performed to systematically investigate the hot-carrier dynamics in an array of graphene samples. The theory calculates explicitly the time-dependent response of the system to a THz probe pulse. The calculations reveal that the observed dynamics can be accounted for qualitatively without including any fitting parameters, phenomenological models or extrinsic effects. Specifically, the hot-carrier dynamics are governed by the coupling of extraordinarily efficient carrier-carrier and carrier-phonon interactions. Furthermore, the theory demonstrates that the simple Drude model is insufficient to fully account for the THz interactions.Beside pump-probe studies, the thesis presents the absorption spectra of mono-and bilayer graphene including the impact of the fully momentum-dependent optical and Coulomb matrix elements. In agreement with recent experiments, the absorbance of graphene is characterized by a frequency-independent value in the near-infrared spectral region and a pronounced peak in the ultraviolet region resulting from interband transition. In contrast to the linear band structure of graphene, the energy dispersion of bilayer graphene exhibits four parabolic bands resulting in interesting optical features: The absorbance exhibits in...

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Carrier multiplication in graphene under Landau quantization

Cited by 64 publications

References 37 publications

Experimentally accessible signatures of Auger scattering in graphene

Experimentally accessible signatures of Auger scattering in graphene

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Relaxation Dynamics in Graphene

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