讲座预告 | 乌得勒支大学王海教授：Negative Photoconductivity as a Signature of Many-Body Interactions in Nanomaterials Studied by THz Spectroscopy

报  告 人：王    海 教授 （乌得勒支大学）

邀  请 人：陈东成 教授

报告时间：1月22日（周四）下午3:00-4:30

报告地点：北区科技园1号楼501会议室

报告摘要：

The conversion of light into electrical currents is a fundamental process underlying the operation of a wide range of optoelectronic devices. Understanding the underlying photophysics—such as the generation and transport of charge carriers in photoactive materials following photoexcitation—is essential for improving their energy conversion efficiency. Layered two-dimensional (2D) materials have emerged as key building blocks for next-generation electronic and optoelectronic technologies. In this talk, I will first provide an overview of ultrafast terahertz (THz) spectroscopy and demonstrate its utility as a contactfree technique for characterizing charge-carrier transport in low-dimensional materials¹. I will then discuss how many-body interactions—such as exciton formation in doped monolayers, strong photothermal effects in metallic 2D materials, and charge transfer across van der Waals interfaces—can lead to an unusual pump-induced suppression of conductivity. This phenomenon, termed negative photoconductivity, provides unique insight into non- equilibrium carrier, phonon interactions and dynamics. Finally, I will briefly discuss the implications and relevance of these findings for organic 2D systems. 

报告人简介：

Hai Wang studied materials science at Zhejiang University and obtained his degree in 2009. Between 2009 and 2011, he finished a joint master program in nanoscience at University of Leuven (2009- 2010) in Belgium and Delft University of Technology in the

Netherlands (2010-2011), supported by the Erasmus Mundus fellowship. From 2012, Hai started his PhD at Max Planck Institute for Polymer Research (MPI-P) in Mainz with the support of a fellowship from MAINZ (graduate school of excellence, materials science in Mainz). In his PhD, Hai worked with Prof. dr. Mischa Bonn to investigate ultrafast charge transfer processes at oxide interfaces, and graduated with the highest honor in 2016. After spending 1 year in the group of Mathias Kläui at University of Mainz as a postdoc, Hai started his independent research group “Nano- optoelectronic materials” in the Molecular Spectroscopy department at MPI-P in 2017, and further moved to Utrecht University as a tenured assistant professor in 2023. Employing time-resolved, ultrafast spectroscopies (THz spectroscopy, transient absorption etc.), the central theme of Hai’s current research lies in understanding fundamental charge carrier dynamics and low-energy excitations in solid-state low-dimensional materials and interfaces, relevant for energy and optoelectronic applications.