[staff-physics-and-astronomy-HL-UHD-UD] Announcement for a seminar by dr. Hai Wang (UU) on June 18 - 13.30 In Spectrum 5

[Beta NAT Secretariaat]

Dear all,
We have a visitor coming to the PCM section in a couple of weeks and he will be giving a talk that may be of interest to many within the department.
Best wishes,
Andrea


Announcement: Seminar by dr. Hai Wang (UU)

Date: Thursday, June 18, 2026
Time: 13:30 - 14:30
Place: Spectrum 5, VU Amsterdam

Title
Ultrafast Snapshots of Charge and Energy Dynamics in Low-Dimensional Materials Using THz Spectroscopy

Speaker
Hai Wang
Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, the Netherlands
Max Planck Institute for Polymer Research, Mainz, Germany

Abstract
The conversion of light into electrical current underpins varied technologies such as photovoltaics and photodetectors. Understanding how charge carriers are generated and transported in the ultrafast (e.g from ps to ns time scale) is critical, as these processes determine recombination pathways, energy losses, and ultimately device performance. Layered two-dimensional (2D) materials have emerged as promising platforms for next-generation optoelectronic devices. Since the discovery of graphene, the family of 2D materials has expanded rapidly to encompass a wide range of electronic phases, including metallic systems (e.g., graphene, MXenes), semiconductors (e.g., transition metal dichalcogenides), and insulators (e.g., hexagonal boron nitride). Their reduced dimensionality and strong many-body interactions provide an ideal setting for investigating ultrafast charge-carrier and energy flow dynamics in nonequilibrium regimes. In this talk, I will first introduce the fundamentals of ultrafast terahertz (THz) spectroscopy and highlight its power as a contact-free probe of charge transport properties¹ and low-energy excitations² in low-dimensional materials. I will then present two recent studies: one exploring the ultrafast generation of free carriers in strongly excitonic systems through hot-carrier-assisted exciton dissociation³, and another investigating strong photothermal transport in 2D metallic MXenes with markedly slow thermal energy dissipation⁴. Together, these examples demonstrate how ultrafast THz spectroscopy provides unique insight into the fundamental processes in low-dimensional quantum materials. Our work further reveals the pivotal role of many-body (e.g. carrier-carrier and carrier-phonon) interactions in dictating ultrafast charge and energy follow dynamics in nanomaterials for light harvesting and sensing applications.

References
1. Wenhao Zheng et al., Band Transport by Large Fröhlich Polarons in MXenes, Nature Physics 2022, 18, 544-550.
2. Alexander Tries et al., Experimental Observation of Strong Exciton Effects in Graphene Nanoribbons, Nano Letters 2020, 20, 5, 2993–3002.
3. Guanzhao Wen et al., Hot Exciton Dissociation in Graphene Nanoribbons, Nature Communications 2026, in press.
4. Wenhao Zheng et al., Photothermal effects control ultrafast charge transport in titanium carbide MXenes, Nature Communications 2026, 17, 1201.

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