Lecture Fulvio Parmigiani
|16 March 2011||FWN-Building 5114.0004, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Prof. Dr. Fulvio Parmigiani|
|Affiliation:||Physics Department, University of Trieste, Italy|
|Title:||Ultrafast electronic response and photoinduced charge transfer at the graphite surface|
|Date:||Wed Mar 16, 2011|
|Telephone:||+31 50 363 4736|
In these last decades it has been demonstrated that the optical properties of semiconductors near the electronic band-gap are dominated by excitons and their residual interactions, producing many-body effects, such as band-gap renormalization (BGR), and nonlinear optical mechanisms. In particular, a deep insight has been gained on understanding the BGR in semiconductors by means of time-resolved non-linear optical spectroscopy in the femtosecond time-domain. For these reasons semiconductors have been considered ideal materials for such studies.
Instead, in semi-metallic and gap-less systems the response to strong photo-excitations is still unclear, and the studies of the dynamics and interactions of quasi-particles have been only marginal.
Starting from these considerations we focus our experiments on measuring, by non-linear angle resolved photoemission, the effective mass and line-width of the IPS in highly oriented pyrolitic graphite (HOPG) sample excited by ~100 fs laser pulses. By tuning the photon energy across the p -bands saddle points, located at the M point of the Brillouin Zone (BZ), i.e. the van Hove singularity (vHs), we photo-inject a high carriers density (~2 x1020 cm-3) in the outermost graphene layers.
Here, by showing the strong correlation among the IPS electron effective mass, the IPS total full-width and the IPS emission intensity versus the photon energy we unveil the electron dynamics and the band renormalization effects governing the correlated interactions of the unoccupied states in graphite. On the basis of these observations we formulate a consistent self-energy model that connects by causality, via Kramers-Kronig transforms, the IPS effective mass with the IPS total full-width, predicting a transient bands energy renormalization mechanism consistent with the experimental observations.
|Last modified:||22 October 2012 2.30 p.m.|