Plasmonic hot carrier injection from single gold nanoparticles into topological insulator Bi₂Se₃ nanoribbons

Plasmonic gold nanoparticles injecting hot carriers into the topological insulator (TI) interface of Bi₂Se₃ nanoribbons are studied by resonant Raman spectroscopy. We resolve the impact of individual gold particles with sizes ranging from 140 nm down to less than 40 nm on the topological surface states of the nanoribbons. In resonance at 1.96 eV (633 nm), we find distinct phonon renormalization in the E_g²- and A_1g²-modes that can be associated with plasmonic hot carrier injection. The phonon modes are strongly enhanced by a factor of 350 when tuning the excitation wavelengths into interband transition and in resonance with the surface plasmon of gold nanoparticles. At 633 nm wavelength, a plasmonic enhancement factor of 18 is observed indicating a contribution of hot carriers injected from the gold nanoparticles into the TI interface. Raman studies as a function of gold nanoparticle size reveal the strongest hot carrier injection for particles with size of 108 nm in agreement with the resonance energy of its surface plasmon. Hot carrier injection opens the opportunity to locally control the electronic properties of the TI by metal nanoparticles attached to the surface of nanoribbons.