Terahertz emission spectroscopy of mid-infrared active photocurrent dynamics in Weyl semimetals

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K15198
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 30020:Optical engineering and photon science-related
• Research Institution: The University of Tokyo
• Principal Investigator: Soutome Masato 東京大学, 先端科学技術研究センター, 特任助教 (40783999)
• Project Period (FY): 2020-04-01 – 2022-03-31
• Keywords: シフト電流 / 光電流 / 太陽電池 / テラヘルツ / 超高速分光 / 半導体

Outline of Final Research Achievements

Photocurrent in semiconductors is widely used in photodetectors and solar cells. Recently, quantum mechanical theory of semiconductors proposed that shift-current, in which the electron cloud propagates coherently instantly, can be the basis of a new type solar cell. In this study, we experimentally evaluated the sub-picosecond dynamics of shift-current and its amplitude by observing terahertz electromagnetic waves emitted from the shift-current. We clarified ultrafast dynamics of photocurrent in a prototypical semiconductor CdS. We measured the excitation photon energy dependence (0.5-2.6 eV) of terahertz emission, and found a peak structure on its exciton resonance.

Free Research Field

光物性物理学

Academic Significance and Societal Importance of the Research Achievements

シフト電流のモデル物質として、化合物半導体CdSにおける励起子共鳴励起でのシフト電流ダイナミクスを観測することに成功した。シフト電流の励起光子エネルギー依存性に励起子共鳴でピークが見られ、その振幅がシフト電流の理論と定量的に一致することを見出した初めての研究である。将来の光電変換デバイス（太陽電池・光検出器など）の基本原理となる現象について電極などの影響を受けずに観測できることを示した。