Gapped Surface States in a Strong-Topological-Semimetal

Abstract

A three-dimensional strong-topological-insulator or -semimetal hosts topological surface states which are often said to be gapless so long as time-reversal symmetry is preserved. This narrative can be mistaken when surface state degeneracies occur away from time-reversal-invariant momenta. The mirror-invariance of the system then becomes essential in protecting the existence of a surface Fermi surface. Here we show that such a case exists in the strong-topological-semimetal Bi${}_4$Se${}_3$. Angle-resolved photoemission spectroscopy and \textit{ab initio} calculations reveal partial gapping of surface bands on the Bi${}_2$Se${}_3$-termination of Bi${}_4$Se${}_3$(111), where an 85 meV gap along $\bar{\Gamma }\bar{K}$ closes to zero toward the mirror-invariant $\bar{\Gamma }\bar{M}$ azimuth. The gap opening is attributed to an interband spin-orbit interaction that mixes states of opposite spin-helicity.

5 pages, 3 figures

References in corpus (5)

• Topological Insulators with Inversion Symmetry
• Topological Crystalline Insulators
• First direct observation of Spin-textures in Topological Insulators : Spin-resolved ARPES as a probe of topological quantum spin Hall effect and Berry's phase
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Cited by in corpus (1)

• Robust Dual Topological Character with Spin-Valley Polarization in a Monolayer of the Dirac Semimetal Na${}_3$Bi