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| VOLUME 96 (2012) | ISSUE 12 | PAGE 870 |
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New topological surface state in layered topological insulators: unoccupied Dirac cone
S. V. Eremeev+*, I. V. Silkin*, T. V. Menshchikova*, A. P. Protogenov×, E. V. Chulkov°∇
+Institute of Strength Physics and Materials Science of the SB of the RAS, 634021 Tomsk, Russia *Tomsk State University, 634050 Tomsk, Russia ×Institute of Applied Physics of the RAS, 603950 N.Novgorod, Russia °Donostia International Physics Center, 20018 San Sebastián, Basque Country, Spain ∇Departamento de Física de Materiales UPV/EHU and Centro de Física de Materiales CFM and Centro Mixto CSIC-UPV/EHU, 20080 San Sebastián/Donostia, Basque Country, Spain
Abstract
The unoccupied states in topological insulators Bi2Se3, PbSb2Te4, and Pb2Bi2Te2S3 are studied by the density functional theory methods. It is shown that a surface state with linear dispersion emerges in the inverted conduction band energy gap at the center of the surface Brillouin zone on the (0001) surface of these insulators. The alternative expression of  invariant allowed us to show that a
necessary condition for the existence of the second 
Dirac cone is the presence of local gaps at the time reversal
invariant momentum points of the bulk spectrum and change of parity
in one of these points.
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