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 1.52eV and a significant Fermi level shift of 0.12eV 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. Condensed-matter physics: mapping temperature changesThe temperature dependence of plasmons, exotic particles of light and matter, in topological insulators has been mapped by researchers in Singapore, France and the US. Topological insulators can conduct an electrical current on their surface even though they are insulators on the inside. This gives rise to unusual properties, such as effectively massless electrons. Andrivo Rusydi and Thomas Whitcher from the National University of Singapore and co-workers have investigated how the long-range interactions between these electrons change with temperature. They used numerous state-of-the-art experimental techniques to map the possible energy levels of the electrons in the topological insulator bismuth selenide. The results, supported by numerical calculations, provided evidence of the existence of plasmons: particles created when electrons strongly couple to light. Long-range plasmon interactions could be useful in plasmonics, a form of information processing. Using a combination of angle-dependent spectroscopic ellipsometry and angle-resolved photoemission spectroscopy as a function of temperature and supported by first-principles calculations, we reveal a new pair of correlated plasmonic excitations at 1.04 and 1.52eV and a significant Fermi level shift of 0.12eV, 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.