Journal article

Ultrafast nonequilibrium evolution of excitonic modes in semiconductors

  • Murakami, Yuta Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo, Japan - Department of Physics, University of Fribourg, Switzerland
  • Schüler, Michael Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, California, USA
  • Takayoshi, Shintaro Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
  • Werner, Philipp Department of Physics, University of Fribourg, Switzerland
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Published in:
  • Physical Review B. - 2020, vol. 101, no. 3, p. 035203
English We study the time evolution of excitonic states after photoexcitation in the one- dimensional spinless extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym ansatz (GKBA) implemented with the 2BA, and the infinite time-evolving block decimation (iTEBD) method. It is found that the GKBA gives the best agreement with iTEBD and captures the relevant physics. Excitations to the particle-hole continuum and resonant excitations of the equilibrium exciton result in a qualitatively different dynamics. In the former case, the exciton binding energy remains positive and the frequency of the corresponding coherent oscillations is smaller than the band gap. On the other hand, resonant excitations trigger a collective mode whose frequency is larger than the band gap. We discuss the origin of these different behaviors by evaluating the nonequilibrium susceptibility using the nonthermal distribution and a random phase approximation. The peculiar mode with frequency larger than the band gap is associated with a partial population inversion with a sharp energy cutoff. We also discuss the effects of the cooling by a phonon bath. We demonstrate the real-time development of coherence in the polarization, which indicates excitonic condensation out of equilibrium.
Faculté des sciences et de médecine
Département de Physique
  • English
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