Ultrafast Dynamics of Massive Dirac Fermions in Bilayer Graphene

作者：Ulstrup Soren^*; Johannsen Jens Christian; Cilento Federico; Miwa Jill A; Crepaldi Alberto; Zacchigna Michele; Cacho Cephise; Chapman Richard; Springate Emma; Mammadov Samir; Fromm Felix; Raidel Christian; Seyller Thomas; Parmigiani Fulvio; Grioni Marco; King Phil D C; Hofmann Philip

来源：Physical Review Letters, 2014, 112(25): 257401.

DOI：10.1103/PhysRevLett.112.257401

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%26apos;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.

• 出版日期2014-6-25