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  Snapshots of non-equilibrium Dirac carrier distributions in graphene

Gierz, I., Petersen, J. C., Mitrano, M., Cacho, C., Turcu, E., Springate, E., et al. (2013). Snapshots of non-equilibrium Dirac carrier distributions in graphene. Nature Materials, 12(12), 1119-1124. doi:10.1038/nmat3757.

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© I. Gierz et al.

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http://dx.doi.org/10.1038/nmat3757 (Publisher version)
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http://arxiv.org/abs/1304.1389 (Preprint)
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 Creators:
Gierz, Isabella1, 2, Author           
Petersen, Jesse C.1, 3, Author           
Mitrano, Matteo1, Author           
Cacho, C.4, Author
Turcu, E.4, Author
Springate, E.4, Author
Stöhr, A.5, Author
Köhler, A.5, Author
Starke, U.5, Author
Cavalleri, Andrea1, 3, Author           
Affiliations:
1Quantum Condensed Matter Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, Luruper Chaussee 149, Geb. 99 (CFEL), 22761 Hamburg, DE, ou_1938293              
2Ultrafast Electron Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, Luruper Chaussee 149, Geb. 99 (CFEL), 22761 Hamburg, DE, ou_1938295              
3Department of Physics, Clarendon Laboratory, University of Oxford, OX1 3PU Oxford, UK, ou_persistent22              
4Central Laser Facility, STFC Rutherford Appleton Laboratory, OX11 0QX Harwell, UK, ou_persistent22              
5Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany, ou_persistent22              

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 Abstract: The optical properties of graphene are made unique by the linear band structure and the vanishing density of states at the Dirac point. It has been proposed that even in the absence of a bandgap, a relaxation bottleneck at the Dirac point may allow for population inversion and lasing at arbitrarily long wavelengths. Furthermore, efficient carrier multiplication by impact ionization has been discussed in the context of light harvesting applications. However, all of these effects are difficult to test quantitatively by measuring the transient optical properties alone, as these only indirectly reflect the energy- and momentum-dependent carrier distributions. Here, we use time- and angle-resolved photoemission spectroscopy with femtosecond extreme-ultraviolet pulses to directly probe the non-equilibrium response of Dirac electrons near the K-point of the Brillouin zone. In lightly hole-doped epitaxial graphene samples, we explore excitation in the mid- and near-infrared, both below and above the minimum photon energy for direct interband transitions. Whereas excitation in the mid-infrared results only in heating of the equilibrium carrier distribution, interband excitations give rise to population inversion, suggesting that terahertz lasing may be possible. However, in neither excitation regime do we find any indication of carrier multiplication, questioning the applicability of graphene for light harvesting.

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Language(s): eng - English
 Dates: 2013-04-162013-07-202013-10-062013-12
 Publication Status: Issued
 Pages: 6
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1038/nmat3757
arXiv: 1304.1389
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Title: Nature Materials
  Abbreviation : Nat. Mater.
Source Genre: Journal
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Publ. Info: London, UK : Nature Pub. Group
Pages: - Volume / Issue: 12 (12) Sequence Number: - Start / End Page: 1119 - 1124 Identifier: ISSN: 1476-1122
CoNE: https://pure.mpg.de/cone/journals/resource/111054835734000