Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy

Scanning tunneling spectroscopic studies of Bi2Se3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level (EFEF) and the Dirac point (EDED) and diverges as EFEF approaches EDED. The Dirac-cone surface state of the host recovers within ∼2 Å spatial distance from impurities, suggesting robust topological protection of the surface state of topological insulators against high-density impurities that preserve time reversal symmetry.

► We study the Fermi-energy dependent impurity resonances in topological insulators.
► We observe sharp impurity resonances at energies near the Dirac point.
► The strength of resonances increases as the Fermi level approaches the Dirac point.
► The impurity resonances are spatially localized within a lattice constant.
► Theoretical modeling of impurity effects on Dirac fermions agree with experiments.