Tunable Carrier Multiplication and Cooling in Graphene

Johannsen, J.; Ulstrup, Søren; Crepaldi, Alberto; Cilento, Federico; Zacchigna, M.; Miwa, Jill A.; Cacho, Céphise; Chapman, Richard T.; Springate, E.; Fromm, Felix; Raidel, Christian; Seyller, Thomas; King, P. D. C.; Parmigiani, F.; Grioni, M.; Hofmann, Philip

doi:10.1021/nl503614v

Cited by 100 publications

(126 citation statements)

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“…Direct comparison to experimental data: After having presented the theoretical results on the doping dependence of the carrier multiplication, a direct comparison with recently performed time-resolved ARPES measurements on nand p-doped graphene samples is presented [128]. Considering that the microscopic theory does not contain any tting parameters, an excellent agreement between theory and experiment is obtained, cf.…”

Section: Carrier Multiplication In Doped Graphenementioning

confidence: 81%

“…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: 98%

“…However, an extrinsic carrier density can have a crucial impact on the relaxation dynamics via a signi cant increase in the scattering phase space and the enhanced e ect of Pauli blocking, which causes both the carrier dynamics and consequently also the performance of graphene in opto-eletronic devices. A rst experimental time-resolved ARPES study has been performed addressing the doping dependence of carrier multiplication of graphene [128]. The underlying elementary processes determining the observed di erent behavior for p-and n-doped samples have not been understood, yet.…”

Section: Shortcoming Of the Drude Modelmentioning

confidence: 99%

“…Here, one has to distinguish between the carrier generating impact excitation (IE) and its inverse process, the Auger recombination (AR). In distinct excitation regimes, the IE has a higher probability than AR leading to a theoretically predicted and experimentally con rmed carrier multiplication (CM) [30,128,133,135]. CM is generally de ned as the ratio between the number of overall generated electron-hole pairs and the optically excited charge carriers:…”

Section: Carrier Multiplication In Doped Graphenementioning

confidence: 99%

“…and the associated carrier multiplication for transport phenomena is labeled as hot carrier multiplication (hCM) [101,128], cf. Fig.…”

Section: Carrier Multiplication In Doped Graphenementioning

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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Section: Carrier Multiplication In Doped Graphenementioning

confidence: 81%