Novel low-energy collective excitation at metal surfacesV. M. Silkin, A. García-Lekue, J. M. Pitarke, E. V. Chulkov, E. Zaremba and P. M. EcheniqueEurophys. Lett., 66 2 (2004) 260-264DOI: https://doi.org/10.1209/epl/i2003-10184-1