Correlated plasmons in the topological insulator Bi2Se3 induced by long-range electron correlations

Recently, electron correlation has been shown to play an important role in unconventional plasmon generation in highly correlated electron systems. Electrons in topological insulators, on the other hand, are massless and insensitive to nonmagnetic scattering due to their protection by time-reversal symmetry, which makes these materials appealing platforms for hosting exotic plasmonic excitations. Here, using a combination of angle-dependent spectroscopic ellipsometry and angle-resolved photoemission spectroscopy as a function of temperature supported by first-principles calculations, we reveal a new pair of correlated plasmonic excitations at 1.04 and 1.52 eV and a significant Fermi level shift of 0.12 eV accompanied by spectral weight transfer in the topological insulator bismuth selenide (Bi2Se3). Interestingly, such a spectral weight transfer over a broad energy range causes a drastic change in the charge carrier density whereby the contribution of charge carriers in the bulk starts to rival those in the surface states and Bi2Se3 becomes more uniformly conducting. Our results show the importance of electronic correlations in determining the electronic structure and appearance of correlated plasmons in topological insulators and their potential applications in plasmonics.