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Ultrafast momentum imaging of pseudospin-flip excitations in graphene

S. Aeschlimann ; R. Krause ; M. Chavez-Cervantes ; H. Bromberger ; Roland Jago (Institutionen för fysik, Kondenserade materiens teori (Chalmers)) ; Ermin Malic (Institutionen för fysik, Kondenserade materiens teori (Chalmers)) ; A. Al-Temimy ; C. Coletti ; A. Cavalleri ; I. Gierz
Physical Review B (2469-9950). Vol. 96 (2017), 2,
[Artikel, refereegranskad vetenskaplig]

The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photoexcited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization and are maximum perpendicular to it. Here, we use time-and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy, and in-plane momentum. We first show that the rapidly-established quasithermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb-and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photoexcited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photocontrol experiments and optoelectronic device applications.

Denna post skapades 2017-08-16. Senast ändrad 2017-08-16.
CPL Pubid: 251179


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Institutionen för fysik, Kondenserade materiens teori (Chalmers)


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