Abstract
We present STM/STS, ARPES and magnetotransport studies of the surface topography and electronic structure of pristine Bi2Se3 in comparison to Bi1.96Mg0.04Se3 and Bi1.98Fe0.02Se3. The topography images reveal a large number of complex, triangle-shaped defects at the surface. The local electronic structure of both the defected and non-defected regions is examined by STS. The defect-related states shift together with the Dirac point observed in the undefected area, suggesting that the local electronic structure at the defects is influenced by doping in the same way as the electronic structure of the undefected surface. Additional information about the electronic structure of the samples is provided by ARPES, which reveals the dependence of the bulk and surface electronic bands on doping, including such parameters as the Fermi wave vector. The subtle changes of the surface electronic structure by doping are verified with magneto-transport measurements at low temperatures (200 mK) allowing the detection of Shubnikov-de Haas (SdH) quantum oscillations.
Highlights
Topological insulators (TIs) are a relatively new type of materials that are characterized by the simultaneous occurrence of a bulk energy gap and peculiar metallic surface states
The aim of this paper is to shed some more light on the questions posed above and to determine how: (1) small changes in Bi2Se3 stoichiometry caused by dopants affect the surface topological states, i.e., the characteristic Dirac cone, (2) such small changes in Bi2Se3 stoichiometry affect the volume electronic structure of a TI and determine the Fermi level, in particular, whether its shift from the conduction band to the energy gap would be possible, and (3) the surface electronic states resulting from structural defects respond to the changes of the volume electronic structure caused by dopants of low concentration, i.e., do they shift to the energy gap or not?
The defect-related states shift together with the DP, suggesting that the local electronic structure at the defects is influenced by doping in the same way as the electronic structure of the undefected surface, i.e., the topological surface states are not affected by defects
Summary
Topological insulators (TIs) are a relatively new type of materials that are characterized by the simultaneous occurrence of a bulk energy gap and peculiar metallic surface states. These metallic boundaries originate as a consequence of a topologically nontrivial bulk electronic structure resulting from strong spin-orbit coupling. Such surface states form characteristic Dirac cones (DCs) with linear dispersion relation, spin—momentum locking [1] (chiral spin texture) and topological protection from backscattering on non-magnetic impurities. The formation of surface states by closing the bandgap at the interface is an indispensable mechanism of the transition between systems of different topologies
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