We have investigated plasmonic excitations at the surface of Bi2Se3(0001) via high-resolution electron energy loss spectroscopy. For low parallel momentum transfer q∥, the loss spectrum shows a distinctive feature peaked at 104 meV. This mode varies weakly with q∥. The behavior of its intensity as a function of primary energy and scattering angle indicates that it is a surface plasmon. At larger momenta (q∥∼0.04 Å−1), an additional peak, attributed to the Dirac plasmon, becomes clearly defined in the loss spectrum. Momentum-resolved loss spectra provide evidence of the mutual interaction between the surface plasmon and the Dirac plasmon of Bi2Se3. The proposed theoretical model accounting for the coexistence of three-dimensional doping electrons and two-dimensional Dirac fermions accurately represents the experimental observations. The results reveal novel routes for engineering plasmonic devices based on topological insulators.
A. Politano,V. M. Silkin, I. A. Nechaev, M. S. Vitiello, L. Viti, Z. S. Aliev, M. B. Babanly, G. Chiarello, P. M. Echenique, E. V. Chulkov
Phys. Rev. Lett. 2015, 115, 216802