Surface Collective Modes in the Topological Insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex

A. Kogar, S. Vig, A. Thaler, M. H. Wong, Y. Xiao, D. Reig-I-Plessis, G. Y. Cho, T. Valla, Z. Pan, J. Schneeloch, R. Zhong, G. D. Gu, T. L. Hughes, G. J. Macdougall, T. C. Chiang, P. Abbamonte

Research output: Contribution to journalArticlepeer-review

Abstract

We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex. Our goal was to identify the "spin plasmon" predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ"(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.

Original languageEnglish (US)
Article number257402
JournalPhysical review letters
Volume115
Issue number25
DOIs
StatePublished - Dec 15 2015

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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