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Journal Article

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

MPS-Authors

Aeschlimann,  S.
Ultrafast Electron Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for FreeElectron Laser Science;

Krause,  R.
Ultrafast Electron Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for FreeElectron Laser Science;

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Chavez Cervantes,  M.
Ultrafast Electron Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for FreeElectron Laser Science;
International Max Planck Research School for Ultrafast Imaging & Structural Dynamics (IMPRS-UFAST), Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Bromberger,  H.
Center for FreeElectron Laser Science;
Quantum Condensed Matter Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Cavalleri,  A.
Center for FreeElectron Laser Science;
Quantum Condensed Matter Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

Gierz,  I.
Ultrafast Electron Dynamics, Condensed Matter Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Center for FreeElectron Laser Science;

External Resource
Fulltext (public)

aeschlimann-PhRB-96-020301-2017.pdf
(Publisher version), 2MB

Supplementary Material (public)

supplementary_final.pdf
(Supplementary material), 3MB

Citation

Aeschlimann, S., Krause, R., Chavez Cervantes, M., Bromberger, H., Jago, R., Malić, E., et al. (2017). Ultrafast momentum imaging of pseudospin-flip excitations in graphene. Physical Review B, 96(2): 020301. doi:10.1103/PhysRevB.96.020301.


Cite as: http://hdl.handle.net/21.11116/0000-0007-0F3C-7
Abstract
The chiral character of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photo-excited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization, and are maximum perpendicular to it. This phenomenon gives rise to unconventional hot carrier dynamics that are only partially understood. Here, we use time- and angle-resolved photoemission spectroscopy to investigate the non-thermal physics of such chiral excitations, sampling carrier distributions as a function of energy and in-plane momentum. We rst show that the rapidly-established quasi-thermal electron distribution initally 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 is dependent on the type of static doping. In n-doped graphene, for which photo-excited carriers are generated close to the Fermi level, the anisotropy of the carrier temperature survives far longer than in p-doped graphene. We attribute this to the strong suppression of azimuthal relaxation due to a reduced phase space for optical phonon emission in the n-doped case. These experiments clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photo-control experiments and optoelectronic device applications.