Ultrafast Electron Dynamics in the Topological Insulator Bi2Se3 Studied by Time-Resolved Photoemission Spectroscopy

Jonathan A. Sobota; Shuolong Yang; Dominik Leuenberger; Alexander F. Kemper; James G. Analytis; Ian R. Fisher; Patrick S. Kirchmann; Thomas P. Devereaux; Zhi-Xun Shen

doi:10.1016/j.elspec.2014.01.005

arXiv · 1401.3078

Ultrafast Electron Dynamics in the Topological Insulator Bi2Se3 Studied by Time-Resolved Photoemission Spectroscopy

Jonathan A. Sobota·Shuolong Yang·Dominik Leuenberger·Alexander F. Kemper·James G. Analytis·Ian R. Fisher·Patrick S. Kirchmann·Thomas P. Devereaux·Zhi-Xun Shen

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Abstract

We characterize the topological insulator Bi$_2$Se$_3$ using time- and angle- resolved photoemission spectroscopy. By employing two-photon photoemission, a complete picture of the unoccupied electronic structure from the Fermi level up to the vacuum level is obtained. We demonstrate that the unoccupied states host a second, Dirac surface state which can be resonantly excited by 1.5 eV photons. We then study the ultrafast relaxation processes following optical excitation. We find that they culminate in a persistent non-equilibrium population of the first Dirac surface state, which is maintained by a meta-stable population of the bulk conduction band. Finally, we perform a temperature-dependent study of the electron-phonon scattering processes in the conduction band, and find the unexpected result that their rates decrease with increasing sample temperature. We develop a model of phonon emission and absorption from a population of electrons, and show that this counter-intuitive trend is the natural consequence of fundamental electron-phonon scattering processes. This analysis serves as an important reminder that the decay rates extracted by time-resolved photoemission are not in general equal to single electron scattering rates, but include contributions from filling and emptying processes from a continuum of states.

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Jonathan A. Sobota, Shuolong Yang, Dominik Leuenberger, Alexander F. Kemper, James G. Analytis, Ian R. Fisher, Patrick S. Kirchmann, Thomas P. Devereaux, Zhi-Xun Shen. 2014-02-06. Ultrafast Electron Dynamics in the Topological Insulator Bi2Se3 Studied by Time-Resolved Photoemission Spectroscopy. https://doi.org/10.1016/j.elspec.2014.01.005

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