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dc.contributor.authorTrovatello, Chiara
dc.contributor.authorKatsch, Florian
dc.contributor.authorBorys, Nicholas J.
dc.contributor.authorSelig, Malte
dc.contributor.authorYao, Kaiyuan
dc.contributor.authorBorrego-Varillas, Rocio
dc.contributor.authorScotognella, Francesco
dc.contributor.authorKriegel, Ilka
dc.contributor.authorYan, Aiming
dc.contributor.authorZettl, Alex
dc.contributor.authorSchuck, P. James
dc.contributor.authorKnorr, Andreas
dc.contributor.authorCerullo, Giulio
dc.contributor.authorDal Conte, Stefano
dc.identifier.citationTrovatello, C., Katsch, F., Borys, N. J., Selig, M., Yao, K., Borrego-Varillas, R., ... & Conte, S. D. (2020). The ultrafast onset of exciton formation in 2D semiconductors. Nature communications, 11(1), 1-8.en_US
dc.description.abstractThe equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process.en_US
dc.publisherSpringer Science and Business Media LLCen_US
dc.titleThe ultrafast onset of exciton formation in 2D semiconductorsen_US
mus.citation.journaltitleNature Communicationsen_US
mus.relation.collegeCollege of Letters & Scienceen_US
mus.relation.universityMontana State University - Bozemanen_US

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