QuMat seminar

Ultrafast dynamics of 2D semiconductors and their heterostructures

Speaker: Giulio Cerullo – Politecnico Milano Host: Zeila Zanolli



Layered materials are solids consisting of crystalline sheets with strong in-plane covalent bonds and weak van der Waals out-of-plane interactions. These materials can be easily exfoliated to a single layer, obtaining two-dimensional (2D) materials with radically novel physico-chemical characteristics compared to their bulk counterparts. The field of 2D materials began with graphene and quickly expanded to include semiconducting transition metal dichalcogenides (TMDs). 2D materials exhibit very strong light-matter interaction and exceptionally intense nonlinear optical response, enabling a variety of novel applications in optoelectronics and photonics. Furthermore, stacking 2D materials into heterostructures (HS) offers unlimited possibilities to design new materials tailored for applications. In such HS the electronic structure of the individual layers is well retained because of the weak interlayer van der Waals coupling. Nevertheless, new physical properties and functionalities arise beyond those of their constituent blocks, depending on the type, the stacking sequence and the twist angle of the layers.

This talk will review our recent studies on the ultrafast non-equilibrium optical response of TMDs and their HS. Using high time resolution ultrafast transient absorption (TA) spectroscopy, we monitor the ultrafast onset of exciton formation in TMDs [1] and the dynamics of strongly coupled phonons [2, 3]. Using helicity resolved TA spectroscopy we time-resolve intravalley spin-flip processes [4]. In HS of TMDs we measure ultrafast interlayer hole transfer [5], interlayer exciton formation [6] and use two-dimensional electronic spectroscopy to dissect interlayer electron and hole transfer processes [7].

[1] C. Trovatello et al., Nature Commun. 11, 5277 (2020).
[2] C. Trovatello et al., ACS Nano 14, 5700-5710 (2020).
[3] C. Sayers et al., Nano Lett. 23, 9235–9242 (2023).
[4] Z. Wang et al., Nano Lett. 18, 6882-6891 (2018).
[5] Z. Wang et al., Nano Lett. 21, 2165–2173 (2021).
[6] V. Policht et al., Nature Commun. 14, 7273 (2023).
[7] V. Policht et al., Nano Lett. 21, 4738–4743 (2021).

Giulio Cerullo is a Full Professor with the Physics Department, Politecnico di Milano, where he leads the Ultrafast Optical Spectroscopy laboratory. Prof. Cerullo’s research activity covers a broad area known as “Ultrafast Optical Science”, and concerns on the one hand pushing our capabilities to generate and manipulate ultrashort light pulses, and on the other hand using such pulses to capture the dynamics of ultrafast events in molecular and solid-state systems. He has published over 500 papers which have received >30000 citations (H-index: 88 on Scopus). He is a Fellow of the Optical Society of America, of the European Physical Society and of the Accademia dei Lincei and past Chair of the Quantum Electronics and Optics Division of the European Physical Society. He is the recipient of an ERC Advanced Grant (2012-2017) on two-dimensional electronic spectroscopy of biomolecules. He has been General Chair of the conferences CLEO/Europe 2017, Ultrafast Phenomena 2018 and the International Conference on Raman Spectroscopy 2020. In 2023, he received the Quantum Electronics Prize of the European Physical Society. He is the co-founder of two spin off companies (NIREOS and Cambridge Raman Imaging).

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