Microscopic theory of absorption and ultrafast many-particle kinetics in graphene

Malić, Ermin; Winzer, Torben; Bobkin, Evgeny; Knorr, Andreas

doi:10.1103/physrevb.84.205406

Cited by 291 publications

(469 citation statements)

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“…We note here that this experimental geometry implies that we are probing along a maximum of the initially anisotropic photo-injected carrier distribution 27 that re-distributes itself into an isotopic distribution on the time scale of the carrier thermalization. 6,27,28 The sample temperature was fixed at 300 K, and the total time, energy and angular resolution were better than 40 fs, 200 meV and 0.3 • , respectively. fs and 600 fs).…”

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confidence: 99%

Tunable Carrier Multiplication and Cooling in Graphene

et al. 2014

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Time-and angle-resolved photoemission measurements on two doped graphene samples displaying different doping levels reveal remarkable differences in the ultrafast dynamics of the hot carriers in the Dirac cone. In the more strongly (n-)doped graphene, we observe larger carrier multiplication factors (> 3) and a significantly faster phonon-mediated cooling of the carriers back to equilibrium compared to in the less (p-)doped graphene. These results suggest that a careful tuning of the doping level allows for an effective manipulation of graphene's dynamical response to a photoexcitation.

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Tunable Carrier Multiplication and Cooling in Graphene

et al. 2014

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“…A variety of dynamical phenomena, such as the appearance of a signi cant carrier multiplication and transient optical gain, have been theoretically predicted [30 33] and experimentally con rmed [32,34,35]. A consistent treatment of the relaxation dynamics containing all important scattering contributions can be realized within the density matrix approach [17,36,37]. 1.…”

Section: Motivationmentioning

confidence: 99%

“…In graphene, a linearly polarized ultrafast optical pulse excitation gives rise to an initially anisotropic distribution of carriers at high energy [28,29]. The e cient carrier-carrier and carrier-phonon scattering processes quickly relax the hot carriers into an isotropic thermal distribution, which is then followed by carrier cooling due to carrier-phonon processes [17,22,23]. A variety of dynamical phenomena, such as the appearance of a signi cant carrier multiplication and transient optical gain, have been theoretically predicted [30 33] and experimentally con rmed [32,34,35].…”

Section: Motivationmentioning

confidence: 99%

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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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2013

Graphene and Carbon Nanotubes

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Microscopic theory of absorption and ultrafast many-particle kinetics in graphene

Cited by 291 publications

References 47 publications

Tunable Carrier Multiplication and Cooling in Graphene

Tunable Carrier Multiplication and Cooling in Graphene

Relaxation Dynamics in Graphene

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