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

Journal Article · 19 August 2021 · Ultrafast Science

DOI: https://doi.org/10.34133/2021/9820716 · OSTI ID:1909244

Kobayashi, Yuki  ^[1]; Heide, Christian  ^[1]; Kelardeh, Hamed Koochaki  ^[2]; Johnson, Amalya  ^[3]; Liu, Fang  ^[4]; Heinz, Tony F.  ^[5]; Reis, David A.  ^[5]; Ghimire, Shambhu  ^[6]

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1. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025USA, Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
2. Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 DresdenGermany
3. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
4. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025USA, Department of Chemistry, Stanford University, Stanford, CA 94305, USA
5. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025USA, Department of Applied Physics, Stanford University, Stanford, CA 94305, USA, Department of Photon Science, Stanford University, Stanford, CA 94305, USA
6. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025USA

We present a systematic study of the crystal-orientation dependence of high-harmonic generation in monolayer transition-metal dichalcogenides, WS ₂ and MoSe ₂ , 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 WS ₂ , 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 MoSe ₂ 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.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1909244
• Journal Information: Ultrafast Science, Journal Name: Ultrafast Science Vol. 2021; ISSN 2765-8791
• Publisher: American Association for the Advancement of Science (AAAS)Copyright Statement
• Country of Publication: United States
• Language: English