| 1. |
- Mihnev, M. T., et al.
(författare)
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Microscopic origins of the terahertz carrier relaxation and cooling dynamics in graphene
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 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. |
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| 4. |
- Jago, Roland, 1990, et al.
(författare)
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Graphene as gain medium for broadband lasers
- 2015
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:8
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Tidskriftsartikel (refereegranskat)abstract
- Efficient nonradiative carrier recombination strongly counteracts the appearance of optical gain in graphene. Based on a microscopic and fully quantum-mechanical study of the coupled carrier, phonon, and photon dynamics in graphene, we present a strategy to obtain a long-lived gain: Integrating graphene into a high quality photonic crystal nanocavity and applying a high-dielectric substrate suppresses the nonradiative recombination channels and gives rise to pronounced coherent light emission. This suggests the design of graphene-based laser devices covering a broad spectral range.
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| 5. |
- Jago, Roland, 1990, et al.
(författare)
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Recombination channels in optically excited graphene
- 2015
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 252:11, s. 2456-2460
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical study on the efficiency of non-radiative recombination channels in optically excited graphene on a substrate. We find that depending on the strength of the excitation pulse and the dielectric constant of the applied substrate, either Auger or phonon-induced recombination prevails. The favorable conditions for Auger recombination are (i) strong excitation regime providing a large number of scattering partners and (ii) low-dielectric substrates, which only weakly screen the Coulomb interaction. The gained insights are important for achieving a population inversion in graphene that is temporally limited by the presented recombination channels.
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| 6. |
- Kadi, Faris, et al.
(författare)
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Impact of doping on the carrier dynamics in graphene
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 5, s. 7-
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Tidskriftsartikel (refereegranskat)abstract
- We present a microscopic study on the impact of doping on the carrier dynamics in graphene, in particular focusing on its influence on the technologically relevant carrier multiplication in realistic, doped graphene samples. Treating the time- and momentum-resolved carrier-light, carrier-carrier, and carrier-phonon interactions on the same microscopic footing, the appearance of Auger-induced carrier multiplication up to a Fermi level of 300 meV is revealed. Furthermore, we show that doping favors the so-called hot carrier multiplication occurring within one band. Our results are directly compared to recent time-resolved ARPES measurements and exhibit an excellent agreement on the temporal evolution of the hot carrier multiplication for n- and p-doped graphene. The gained insights shed light on the ultrafast carrier dynamics in realistic, doped graphene samples.
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| 7. |
- 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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| 8. |
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| 9. |
- Malic, Ermin, 1980, et al.
(författare)
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Review on carrier multiplication in graphene
- 2016
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 253:12, s. 2303-2310
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Tidskriftsartikel (refereegranskat)abstract
- The remarkable gapless and linear band structure of graphene opens up new carrier relaxation channels bridging the valence and the conduction band. These Auger scattering processes change the number of charge carriers and can give rise to a significant multiplication of optically excited carriers in graphene. This is an ultrafast many-particle phenomenon that is of great interest both for fundamental many-particle physics as well as technological applications. Here, we review the research on carrier multiplication in graphene and Landau-quantized graphene including theoretical modeling and experimental demonstration. Illustration of the electronic band structure of graphene including Auger scattering channels that can lead to a carrier multiplication (CM). Figure adapted from Ref. [2].
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| 10. |
- Schneider, E, et al.
(författare)
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CD73-mediated adenosine production by CD8 T cell-derived extracellular vesicles constitutes an intrinsic mechanism of immune suppression
- 2021
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1, s. 5911-
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Tidskriftsartikel (refereegranskat)abstract
- Immune cells at sites of inflammation are continuously activated by local antigens and cytokines, and regulatory mechanisms must be enacted to control inflammation. The stepwise hydrolysis of extracellular ATP by ectonucleotidases CD39 and CD73 generates adenosine, a potent immune suppressor. Here we report that human effector CD8 T cells contribute to adenosine production by releasing CD73-containing extracellular vesicles upon activation. These extracellular vesicles have AMPase activity, and the resulting adenosine mediates immune suppression independently of regulatory T cells. In addition, we show that extracellular vesicles isolated from the synovial fluid of patients with juvenile idiopathic arthritis contribute to T cell suppression in a CD73-dependent manner. Our results suggest that the generation of adenosine upon T cell activation is an intrinsic mechanism of human effector T cells that complements regulatory T cell-mediated suppression in the inflamed tissue. Finally, our data underscore the role of immune cell-derived extracellular vesicles in the control of immune responses.
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