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Gapped Surface States in a Strong-Topological-Insulator Material.
A P Weber1, Q D Gibson2, Huiwen Ji2
1Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA.
Physical Review Letters
|July 22, 2015
Summary
Strong topological semimetals can have gapped surface states, contrary to common assumptions. Mirror symmetry protects surface Fermi surfaces, as demonstrated in Bi(4)Se(3) with partial band gapping.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Topological Materials
Background:
- Three-dimensional strong topological insulators and semimetals possess topological surface states.
- These states are often assumed to be gapless when time-reversal symmetry is conserved.
Purpose of the Study:
- To investigate the protective role of mirror symmetry on surface states in topological semimetals.
- To explore cases where surface state degeneracies occur away from time-reversal-invariant momenta.
Main Methods:
- Utilized angle-resolved photoemission spectroscopy (ARPES).
- Performed ab initio calculations.
- Investigated the Bi(4)Se(3) material system, specifically its Bi(2)Se(3) termination.
Main Results:
- Observed partial gapping of surface bands on the Bi(2)Se(3) termination of Bi(4)Se(3)(111).
- An 85 meV gap along the Γ̅K̅ direction was found to close to zero towards the mirror-invariant Γ̅M̅ azimuth.
- Identified an interband spin-orbit interaction as the cause for the gap opening.
Conclusions:
- The study demonstrates that surface Fermi surfaces in topological semimetals can be protected by mirror symmetry, not solely time-reversal symmetry.
- Partial gapping of surface bands in Bi(4)Se(3) highlights a deviation from the conventional understanding of topological surface states.
- Interband spin-orbit interaction plays a crucial role in modifying surface state topology.
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