Spin-resolves ARPES of three-dimensional topological insulators
| Date/Time: | Thursday, 30 Oct 2014 - Thursday, 30 Oct 2014 |
|---|---|
| Location: | PHYSICS Hall Room 3 |
| Phone: | 515-294-5630 |
| Channel: | College of Liberal Arts and Sciences |
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Topological insulators are attracting special attentions because of their unique physical properties owing to the gapless Dirac-cone surface state with an in-plane helical spin structure[1-5]. This peculiar surface state offers a new playground for studying the various quantum phenomena associated with non-trivial topology, and also for developing novel spintoronic devices manipulating the spin polarization. It has been theoretically proposed that the hexagonal warping of the Fermi surface produces a finite out-of-plane spin component. Understanding of the out-of-plane component is of great importance since it is related to various exotic quantum phenomena. A systematic investigation on the relationship between the out-of-plane spin polarization and the Fermi-surface warping is crucial in developing the microscopic understanding of the characteristics of Dirac fermions in topological insulators.
We report here a systematic spin-resolved ARPES [6] experiments for various topological insulators and provide a first definitive experimental evidence for the existence of a universal relationship between the spin polarization and the Fermi-surface warping [7]. We have quantitatively determined the warping strengths for various topological insulators (PbBi2Te4, Bi2Te3, Bi2Se3, and TlBiSe2) through accurate band-structure mappings, and found that stronger Fermi-surface warping leads to a larger out-of-plane spin polarization. Intriguingly, the magnitude of Pz was found to be only half of that expected from the kop theory when the warping is strong, which points to the possible role of many-body effects. Our observation provides an empirical guiding principle for tuning the spin polarization in topological insulators, which would be of interest to application of the spintronics devices.
[1] S. Souma et al., PRL. 106, 216803 (2011). [2] T. Sato et al., Nature Phys. 7, 840 (2011). [3] T. Arakane et al., Nature Commun. 3, 636 (2012). [4] S. Souma et al., PRL. 108, 116801 (2012). [5] S. Souma et al., PRL. 109, 186804 (2012). [6] S. Souma et al., Rev. Sci. Instrum. 81, 095101 (2010). [7] M. Nomura et al., Phys. Rev. B 89, 045134 (2014).