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Title: Femtosecond to picosecond transient effects in WSe2 observed by pump-probe angle-resolved photoemission spectroscopy

Abstract

Time-dependent responses of materials to an ultrashort optical pulse carry valuable information about the electronic and lattice dynamics; this research area has been widely studied on novel two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs) and topological insulators (TIs). We report herein a time-resolved and angle-resolved photoemission spectroscopy (TRARPES) study of WSe2, a layered semiconductor of interest for valley electronics. The results for below-gap optical pumping reveal energy-gain and -loss Floquet replica valence bands that appear instantaneously in concert with the pump pulse. Energy shift, broadening, and complex intensity variation and oscillation at twice the phonon frequency for the valence bands are observed at time scales ranging from the femtosecond to the picosecond and beyond. Furthermore, the underlying physics is rich, including ponderomotive interaction, dressing of the electronic states, creation of coherent phonon pairs, and diffusion of charge carriers – effects operating at vastly different time domains.

Authors:
 [1];  [1];  [2];  [3];  [1];  [1];  [1];  [1]; ORCiD logo [1];  [1];  [4];  [1]
  1. The Univ. of Tokyo, Chiba (Japan)
  2. Univ. of Illinois at Urbana-Champaign, Urbana, IL (United States)
  3. Tokyo Institute of Technology, Tokyo (Japan)
  4. The Univ. of Tokyo, Chiba (Japan); Univ. of Illinois at Urbana-Champaign, Urbana, IL (United States)
Publication Date:
Research Org.:
Univ. of Illinois at Urbana-Champaign, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1500108
Grant/Contract Number:  
FG02-07ER46383
Resource Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Liu, Ro -Ya, Ogawa, Yu, Chen, Peng, Ozawa, Kenichi, Suzuki, Takeshi, Okada, Masaru, Someya, Takashi, Ishida, Yukiaki, Okazaki, Kozo, Shin, Shik, Chiang, Tai -Chang, and Matsuda, Iwao. Femtosecond to picosecond transient effects in WSe2 observed by pump-probe angle-resolved photoemission spectroscopy. United States: N. p., 2017. Web. doi:10.1038/s41598-017-16076-z.
Liu, Ro -Ya, Ogawa, Yu, Chen, Peng, Ozawa, Kenichi, Suzuki, Takeshi, Okada, Masaru, Someya, Takashi, Ishida, Yukiaki, Okazaki, Kozo, Shin, Shik, Chiang, Tai -Chang, & Matsuda, Iwao. Femtosecond to picosecond transient effects in WSe2 observed by pump-probe angle-resolved photoemission spectroscopy. United States. doi:10.1038/s41598-017-16076-z.
Liu, Ro -Ya, Ogawa, Yu, Chen, Peng, Ozawa, Kenichi, Suzuki, Takeshi, Okada, Masaru, Someya, Takashi, Ishida, Yukiaki, Okazaki, Kozo, Shin, Shik, Chiang, Tai -Chang, and Matsuda, Iwao. Wed . "Femtosecond to picosecond transient effects in WSe2 observed by pump-probe angle-resolved photoemission spectroscopy". United States. doi:10.1038/s41598-017-16076-z. https://www.osti.gov/servlets/purl/1500108.
@article{osti_1500108,
title = {Femtosecond to picosecond transient effects in WSe2 observed by pump-probe angle-resolved photoemission spectroscopy},
author = {Liu, Ro -Ya and Ogawa, Yu and Chen, Peng and Ozawa, Kenichi and Suzuki, Takeshi and Okada, Masaru and Someya, Takashi and Ishida, Yukiaki and Okazaki, Kozo and Shin, Shik and Chiang, Tai -Chang and Matsuda, Iwao},
abstractNote = {Time-dependent responses of materials to an ultrashort optical pulse carry valuable information about the electronic and lattice dynamics; this research area has been widely studied on novel two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs) and topological insulators (TIs). We report herein a time-resolved and angle-resolved photoemission spectroscopy (TRARPES) study of WSe2, a layered semiconductor of interest for valley electronics. The results for below-gap optical pumping reveal energy-gain and -loss Floquet replica valence bands that appear instantaneously in concert with the pump pulse. Energy shift, broadening, and complex intensity variation and oscillation at twice the phonon frequency for the valence bands are observed at time scales ranging from the femtosecond to the picosecond and beyond. Furthermore, the underlying physics is rich, including ponderomotive interaction, dressing of the electronic states, creation of coherent phonon pairs, and diffusion of charge carriers – effects operating at vastly different time domains.},
doi = {10.1038/s41598-017-16076-z},
journal = {Scientific Reports},
number = 1,
volume = 7,
place = {United States},
year = {2017},
month = {11}
}

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Figures / Tables:

Figure 1 Figure 1: Crystal structure, Brillouin zone, and electronic structure of WSe2. (a) Top and side views of the atomic structure of 2H-WSe2. (b) First Brillouin zone and its planar projection. (c) X-ray photoemission spectroscopy data taken from a cleaved WSe2 crystal using 1200-eV photons. (d) Bulk band structure obtained bymore » DFT calculations11.« less

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