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Ultrafast optical spectroscopy of few-layer graphene

Speaker: 
Enrico Da Como (Bath University, UK)
Date: 
Mon, 02/06/2014 - 2:00pm to 3:00pm
Location: 
Graphene Seminar Room (S16 level 6)
Host: 
Goki Eda
Event Type: 
Seminars

Abstract

In this communication, I will talk about how we determine the intrinsic carrier recombination time in exfoliated few-layer samples using femtosecond near-infrared (0.8-0.35 eV photon-energy) pump-probe spectroscopy. The spectra of the different single-flakes (1-, 2-, 3- and 4- layers) show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations of the electronic structure, we assign the photoinduced absorption features to inter-subband transitions as the number of layers is increased. Interestingly, the inter-subband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these inter-subband transitions depends only on the intrinsic carrier lifetime and provides an elegant method to access it in this important class of carbon nanostructures. We report lifetimes from 7 to 5 ps almost independently from the layer number up 4-layer graphene. Above this number of layers the carrier recombination time sets below 4 ps and is identical to what we observe in graphite.

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