138th CEMS Colloquium

Title

Ultrafast Carrier Dynamics in Graphene

Abstract

The study of carrier dynamics in materials and their applications to devices requires high-frequency electrical measurements. However, conventional high-frequency electrical techniques are limited by the frequency bandwidth of the instruments, with a typical time resolution of about 10 ps. This makes it difficult to investigate ultrafast dynamics or to perform time-resolved transport measurements in microscale samples such as exfoliated 2D materials. To overcome this limitation, we have introduced ultrafast laser technology, enabling electrical measurements with sub-picosecond time resolution.

We have applied this technique to 2D materials, and in this presentation, I will report two results obtained in graphene. First, I demonstrate 220-GHz operation of a graphene photodetector, revealing the hot-carrier dynamics induced by optical excitation [1]. Second, I present the propagation control of 1-ps-wide graphene plasmon wavepackets, highlighting their strong spatial confinement, low-loss propagation, and electrical tunability. Our method is highly versatile and has been extended to materials beyond graphene, such as black phosphorus [3] and WTe2 [4]. We aim to further develop this approach to open new research directions in ultrafast carrier dynamics in emerging materials.

In the presentation, I will also give a brief overview of other achievements in our group, including transport measurements on topological materials.

[1] Nat. Photon. 16, 718 (2022).
[2] Nat. Electron. 7, 537 (2024).
[3] arXiv:2506.14550.
[4] under preparation

Contact

email: citonaga@riken.jp
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