Seminars Archive

Ultrafast optical studies of single layer transition metal dichalcogenides and related heterostructures

Abstract
Transition metal dichalcogenides (TMD) are semiconductors exhibiting a transition from indirect to direct bang gap structure when are thinned to a single layer (1L). This property combined with a strong light matter interaction, enhanced by many-body effects, make semiconducting 1L-TMDs forefront materials in the field of electronics, optoelectronics, photonics and energy harvesting research. In addition to that, 1L-TMDs are an ideal platform to study exciton physics even at room temperature: the strong quantum confinement effect and the reduced Coulomb screening, have a deep impact on the 1L-TMD optical response which is dominated by excitons characterized by large binding energy. Moreover, the lower energy excitons are formed at K and K’ valley at the edge of the Brillouin zone and they can be optically addressed by circular polarized light opening up tantalizing possibilities for valleytronics and spintronics applications. In my talk, I will study the non-equilibrium optical response of 1L-TMDs by optical pump-probe spectroscopy. I will show that the non-linear optical response of such materials exhibits strong signature of many body interactions such as band-gap renormalization process. By using time-resolved Faraday rotation and circular dichroism techniques, I will also give an overview of the inter and intravalley relaxation processes occurring in 1L-TMDs. In the last part of the talk, I will show recent results on charge transfer processes occurring in heterostructures realized by vertically stacking two layers of different type of 2D materials. [1] E.A.A. Pogna et al. ACS Nano 10, 1182–1188 (2016). [2] S. Dal Conte et al. Phys. Rev. B 92, 235425 (2015). [3] Z. Wang, et al. Nano Lett. 18, 6882 (2018).