Ultrafast Momentum Imaging of Pseudospin-Flip Excitations in Graphene
| Autor: | Aeschlimann, S., Krause, R., Chávez-Cervantes, M., Bromberger, H., Al-Temimy, A., Coletti, C., Cavalleri, A., Gierz, I. |
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| Rok vydání: | 2017 |
| Předmět: | |
| Zdroj: | Phys. Rev. B 96, 020301 (2017) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.96.020301 |
| Popis: | The pseudospin 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. 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 quasi-thermal 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 photo-excited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photo-control experiments and optoelectronic device applications. Comment: 23 pages, 12 figures |
| Databáze: | arXiv |
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