Volume 2021 Issue 2
Aug.  2021
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Yuki Kobayashi, Christian Heide, Hamed Koochaki Kelardeh, Amalya Johnson, Fang Liu, Tony F. Heinz, David A. Reis, Shambhu Ghimire. 2021: Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides. Ultrafast Science, 2021(2). doi: 10.34133/2021/9820716
Citation: Yuki Kobayashi, Christian Heide, Hamed Koochaki Kelardeh, Amalya Johnson, Fang Liu, Tony F. Heinz, David A. Reis, Shambhu Ghimire. 2021: Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides. Ultrafast Science, 2021(2). doi: 10.34133/2021/9820716

Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides

doi: 10.34133/2021/9820716
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This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division through the AMOS program. F.L. was supported by a Terman Fellowship and startup funds from the Department of Chemistry at Stanford University. Y.K. acknowledges support from the Urbanek-Chodorow Fellowship from Stanford University. C.H. acknowledges support from the W. M. Keck Foundation and a Humboldt Research Fellowship. We thank Dr. S. Azar Oliaei Motlagh for the fruitful discussion on the simulations.

  • Received Date: 2021-04-08
  • Rev Recd Date: 2021-06-25
  • Publish Date: 2021-08-25
  • We present a systematic study of the crystal-orientation dependence of high-harmonic generation in monolayer transition-metal dichalcogenides, WS2 and MoSe2, subjected to intense linearly polarized midinfrared laser fields. The measured spectra consist of both odd- and even-order harmonics, with a high-energy cutoff extending beyond the 15th order for a laser-field strength around ~1 V/nm. In WS2, we find that the polarization direction of the odd-order harmonics smoothly follows that of the laser field irrespective of the crystal orientation, whereas the direction of the even-order harmonics is fixed by the crystal mirror planes. Furthermore, the polarization of the even-order harmonics shows a flip in the course of crystal rotation when the laser field lies between two of the crystal mirror planes. By numerically solving the semiconductor Bloch equations for a gapped-graphene model, we qualitatively reproduce these experimental features and find the polarization flipping to be associated with a significant contribution from interband polarization. In contrast, high-harmonic signals from MoSe2 exhibit deviations from the laser-field following of odd-order harmonics and crystal-mirror-plane following of even-order harmonics. We attribute these differences to the competing roles of the intraband and interband contributions, including the deflection of the electron-hole trajectories by nonparabolic crystal bands.

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