Terahertz sum-frequency excitation of coherent optical phonons in the two-dimensional semiconductor WSe₂

Creators: Kusaba, Satoshi; Lin, Haw-Wei; Tamaki, Ryo; Katayama, Ikufumi; Takeda, Jun; Blake, Geoffrey A.¹

1. California Institute of Technology

Abstract

Driving fundamental excitations via strong light fields is one of the most important issues in solid state physics, which opens up new avenues to control material properties. Two-dimensional materials are fruitful platforms for future semiconductor applications, including opto-electronic and phononic devices, yet the phonon dynamics and nonlinear phonon–phonon coupling remain under-explored. Here, we demonstrate coherent phonon excitation in thin films of the layered two-dimensional semiconductor WSe₂ induced by intense and broadband ultrafast terahertz (THz) pulses. We performed THz Kerr effect spectroscopy and observed coherent phonon oscillations assigned to the E_(2g) optical phonon mode. The phonon amplitude displays a quadratic THz field strength dependence, indicating a sum-frequency THz excitation process. Furthermore, pump–probe polarization and crystal orientation relationships, supported by symmetry analysis of the nonlinear susceptibility and Raman tensors, provide helpful insight into nonlinear phonon–phonon interactions and potential coherent control schemes for the manipulation of phonon polarization and material properties in WSe₂.

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Acknowledgement

H.W.L. acknowledges the financial support from the Ministry of Education of Taiwan. H.W.L. and G.A.B. acknowledge the support by the National Science Foundation CSDM-A Program (Grant No. CHE-1665467) and NASA APRA program (Grant No. 80NSSC21K1467). S.K. and J.T. acknowledge the support by the Grants for Bilateral Collaborations (No. 120209911) and the Grants-in-Aid for Scientific Research (Nos. 20H05662, 22K20354, and 23K13043).

Contributions

Satoshi Kusaba and Haw-Wei Lin contributed equally to this work.

Satoshi Kusaba: Conceptualization (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Haw-Wei Lin: Conceptualization (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Resources (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Ryo Tamaki: Formal analysis (supporting); Investigation (supporting); Methodology (supporting); Supervision (equal); Writing – review & editing (equal). IKufumi Katayama: Funding acquisition (equal); Project administration (equal); Resources (equal); Software (equal); Supervision (equal); Writing – review & editing (equal). Jun Takeda: Funding acquisition (equal); Project administration (equal); Supervision (equal); Writing – review & editing (equal). Geoffrey A. Blake: Funding acquisition (equal); Project administration (equal); Supervision (equal); Writing – review & editing (equal).

Data Availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

See the supplementary material for descriptions of the experimental setup of the TKE spectrometer, preparation, and characterization of the WSe₂ samples with SHG and micro-Raman spectroscopies and complete symmetry analysis of the nonlinear susceptibility and Raman tensors of WSe₂.

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The files will be made publicly available on March 18, 2025.

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Resource type: Journal Article
Publisher: American Institute of Physics
Published in: Applied Physics Letters, 124(12), 122204, ISSN: 0003-6951.
Languages: English