Y. Fuseya

Salle C313 « Nobelium », Bat C, 3eme étage jeudi 28 mars à 14h00

Is Bismuth Topologically Trivial or Not ?

Yuki Fuseya (U. Electro-Communications, Tokyo)

After the proposal of the existence of a three-dimensional topological insulator in Bi_1-xSb_x (Bi-Sb) [1], the surface state (SS) of Bi-Sb has attracted considerable attention in solid-state physics. It has been proposed that Bi-Sb becomes topologically nontrivial for x>0.04 due to band inversion at the L point in a bulk Brillouin zone, while pure Bi is topologically trivial. A drastic change in the SS is therefore expected due to this topological transition [2,3]. Nevertheless, the SS does not exhibit a qualitative change with respect to the Sb substitution even though the bulk conduction and valence band are inverted at x 0.04 [4]. This has been a mystery discussed lively in the fields of both topological physics and surface science.

Here we show a solution to this mystery with an exact solution of the SS of Bi [5]. The size of the gap for the SS of Bi can be larger than that of bulk band gap even for "thick" films (200 bilayers 80 nm) of pure bismuth. Consequently, in such a film of Bi-Sb, there is no apparent change in the SSs through the band inversion, even though the nature of the SS is changed by the topological transition. A possible way to determine the topology of Bi will be discussed as well.

[1] L.Fu, C.L.Kane, Phys. Rev. B 76, 045302 (2007)
[2] D. Hsieh et al., Nature 452, 970 (2008)
[3] D. Hsieh et al., Science 323, 919 (2009)
[4] H. M. Benia et al., Phys. Rev. B 91, 161406 (2015)
[5] Y. Fuseya, H. Fukuyama, J. Phys. Soc. Jpn. 87, 044710 (2018)

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