Here we report the experimental evidence of the interactions between the excitations of the π→π∗ optical transition and the image potential states (IPS) of highly oriented pyrolitic graphite (HOPG). By using non-linear angle resolved photoelectron spectroscopy (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 π→π∗ 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 carriers density (in the 1020 cm−3 range) is created by the absorption of a coherent light pulse. This finding brings a clear evidence of a high IPS-bulk coupling in graphite and opens the way for exploiting the IPS as a sensitive, nonperturbing probe for the many-body dynamics in materials.
@article{arxiv.0910.4473,
title = {First evidence of transient interactions between $\pi\to\pi^*$ optical excitations and image potential states in graphite},
author = {M. Montagnese and S. Pagliara and S. Dal Conte and G. Galimberti and G. Ferrini and F. Parmigiani},
journal= {arXiv preprint arXiv:0910.4473},
year = {2009}
}