Ultrafast dynamics of massive Dirac fermions in bilayer graphene
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Bilayer graphene is a highly promising material for electronic and optoelectronic applications since it is supporting massive Dirac fermions with a tunable band gap. However, no consistent picture of the gap's effect on the optical and transport behavior has emerged so far, and it has been proposed that the insulating nature of the gap could be compromised by unavoidable structural defects, by topological in-gap states, or that the electronic structure could be altogether changed by many-body effects. Here, we directly follow the excited carriers in bilayer graphene on a femtosecond time scale, using ultrafast time- and angle-resolved photoemission. We find a behavior consistent with a single-particle band gap. Compared to monolayer graphene, the existence of this band gap leads to an increased carrier lifetime in the minimum of the lowest conduction band. This is in sharp contrast to the second substate of the conduction band, in which the excited electrons decay through fast, phonon-assisted interband transitions.
Ulstrup , S , Johannsen , J C , Cilento , F , Miwa , J A , Crepaldi , A , Zacchigna , M , Cacho , C , Chapman , R , Springate , E , Mammadov , S , Fromm , F , Raidel , C , Seyller , T , Parmigiani , F , Grioni , M , King , P D C & Hofmann , P 2014 , ' Ultrafast dynamics of massive Dirac fermions in bilayer graphene ' Physical Review Letters , vol 112 , no. 25 , 257401 . DOI: 10.1103/PhysRevLett.112.257401
Physical Review Letters
© 2014 American Physical Society
The authors acknowledge financial support from the VILLUM foundation, The Danish Council for Independent Research/Technology and Production Sciences, the Lundbeck Foundation, the Swiss National Science Foundation (NSF), EPSRC, The Royal Society, and the Italian Ministry of University and Research (Grants No. FIRBRBAP045JF2 and No. FIRB-RBAP06AWK3).
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