Lecture M. Montagnese
|19 November 2009||FWN-Building 5115.0017, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Drs. M. Montagnese|
|Affiliation:||University of Brescia, Italy|
|Title:||Probing the many-body electronic excitations in graphite using image potential states|
|Date:||Thu Nov 19, 2009|
|Host:||P.H.M. van Loosdrecht|
|Telephone:||+31 50 363 8149|
A major challenge in condensed-matter physics is the description of excitations at a level of accuracy comparable to that reached in the description of the ground state. In this framework, the interactions between the excited bulk and the surface electronic structure are still poorly understood. Graphite is an ideal material to perform such a study, given its valence ( pi , pi *) band structure, layered character, and peculiar surface structure. Non linear, angle resolved photoelectron spectroscopy (NL-ARPES) is an ideal technique to perform this task, since it employs intense laser pulses to excite and study the electronic system, giving also access to the empty bulk and surface states.
Here we report the experimental evidence of the interactions between the excitations of the pi-» pi * optical transition and the image potential states (IPS) of highly oriented pyrolitic graphite (HOPG). By using NL-ARPES we show that the IPS photoemission intensity, the effective mass, and the linewidth exhibit a strong variation when the photon energy is tuned across the pi-» pi * saddle points in the 3.1 - 4.5 eV photon energy range. A model based on the self-energy formalism is proposed to correlate the effective mass and the linewidth variations to transient many body effects, when a high carrier density (in the 1020 cm-3 range) is created in the p * band by the absorption of a coherent light pulse. This finding brings a clear evidence of a high IPS-bulk coupling and opens the way for exploiting the IPS as a sensitive, non-perturbing probe for the many-body dynamics in materials.
|Last modified:||22 October 2012 2.30 p.m.|