| 1. |
- Konig-Otto, J. C., et al.
(författare)
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Slow Noncollinear Coulomb Scattering in the Vicinity of the Dirac Point in Graphene
- 2016
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 117:8
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Tidskriftsartikel (refereegranskat)abstract
- The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k directions pointing radially away from the Dirac point. Our study reveals, however, that, in almost intrinsic graphene, full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps time scale. This effect is very promising for infrared and THz devices based on hot carrier effects.
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| 2. |
- Malic, Ermin, 1980, et al.
(författare)
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Carrier Dynamics in Graphene: Ultrafast Many-Particle Phenomena
- 2017
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 529:11
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion.
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| 3. |
- Wendler, Florian, 1982, et al.
(författare)
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Efficient Auger scattering in Landau-quantized graphene
- 2015
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628414516 ; 9361, s. no. 936105-
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Konferensbidrag (refereegranskat)abstract
- We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene.
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| 4. |
- Wendler, Florian, 1982, et al.
(författare)
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Symmetry-Breaking Supercollisions in Landau-Quantized Graphene
- 2017
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 119:6, s. Article no 067405 -
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Tidskriftsartikel (refereegranskat)abstract
- Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealed carrier relaxation times ranging from picoseconds to nanoseconds depending on the quality of the sample. To explain this surprising behavior, we propose a novel symmetry-breaking defect-assisted relaxation channel. This enables scattering of electrons with single out-of-plane phonons, which drastically accelerate the carrier scattering time in low-quality samples. The gained insights provide a strategy for tuning the carrier relaxation time in graphene and related materials by orders of magnitude.
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| 5. |
- Winnerl, S., et al.
(författare)
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Long-lived Anisotropy of Photoexcited Graphene Electrons
- 2016
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Ingår i: 2016 Conference on Lasers and Electro-Optics, CLEO 2016, San Jose, United States, 5-10 June 2016. - 2160-9020. - 9781943580118
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Konferensbidrag (refereegranskat)abstract
- In polarization resolved pump-probe experiments complemented by microscopic modeling we show that an anisotropic carrier distribution persists on ps timescales. In particular, we evaluate the role of non-collinear Coulomb scattering.
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| 6. |
- Winnerl, S., et al.
(författare)
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Ultrafast Processes in Graphene: From Fundamental Manybody Interactions to Device Applications
- 2017
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 529:11
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Tidskriftsartikel (refereegranskat)abstract
- A joint experiment-theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon energy (similar to 200 meV) and the Fermi energy (10-20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon energy. Furthermore, a strongly anisotropic distribution of electrons in k-space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non-collinear Coulomb scattering. Finally, a room temperature operated ultra-broadband hot-electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40ps.
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| 7. |
- Winzer, T., et al.
(författare)
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Unconventional double-bended saturation of carrier occupation in optically excited graphene due to many-particle interactions
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Saturation of carrier occupation in optically excited materials is a well-established phenomenon. However, so far, the observed saturation effects have always occurred in the strong-excitation regime and have been explained by Pauli blocking of the optically filled quantum states. On the basis of microscopic theory combined with ultrafast pump-probe experiments, we reveal a new low-intensity saturation regime in graphene that is purely based on many-particle scattering and not Pauli blocking. This results in an unconventional double-bended saturation behaviour: Both bendings separately follow the standard saturation model exhibiting two saturation fluences; however, the corresponding fluences differ by three orders of magnitude and have different physical origin. Our results demonstrate that this new and unexpected behaviour can be ascribed to an interplay between time-dependent many-particle scattering and phase-space filling effects.
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