Seminars Archive

Ultrafast spectroscopy of 2D materials and related heterostructures

Abstract
The discovery of graphene, the thinnest material ever, has triggered a real revolution into the physics and the technology of the last ten years towards the so called two-dimensional (2D) materials. Different from graphene, which is a gapless semimetal, single layer transition metal dichalcogenides (1L-TMDs), are 2D direct bandgap semiconductors that have recently received significant attention for their potential suitability in photonic and optoelectronic applications. Due to the strong quantum confinement, the optical response of 1L-TMDs is strongly renormalized by excitonic effects. Broadband pump-probe optical spectroscopy is exploited to measure the transient optical response of 1L-MoS₂, around the main excitonic transitions. Coulomb screening, bandgap renormalization and exciton formation processes are investigated both in frequency and in time domain, with unprecedent temporal resolution, i.e. sub-20fs. Graphene and 1L-TMDs can also be stacked together forming the so called Van der Waals heterostructures, which are ideal platforms to tailor electronic/optical properties of new low-dimensional quantum materials. Ultrafast charge transfer processes are also presented in graphene/WS₂ and MoSe2/WSe₂ heterostructures.
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