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Novel interference patterns in Bi2-xFexTe3 observed by scanning tunneling spectroscopy

Topological insulators (TI) have generated much interest lately both from the point of realizing interesting new physics as well as the possibility of being used as materials in quantum computing and spintronic applications. The energy eigenstates of the linearly dispersing surface state band of a topological insulator are composed of degenerate pairs of fermions connected by time reversal (TR) symmetry. Time reversal invariant perturbations are prohibited from mixing these TR paired states. The Introduction of TR breaking perturbations however violates this prohibition. The key prediction that underlies the effects of TR symmetry breaking is the generation of new backscattering processes, which have not yet been directly observed. We have utilized Fourier transform scanning tunneling spectroscopy (FT-STS) to probe the surface of a magnetically doped TI, Bi 2-x Fe x Te 3+d . In the presence of TR breaking Fe impurities, the STM data reveal a new scattering channel. The constraints provided by the magnitude and direction of the multiple scattering vectors clearly identify the new channel with electronic backscattering that would be prohibited in a TR invariant TI. Our combined data present compelling evidence for the first momentum resolved measurement of enhanced backscattering due to magnetic impurities in a prototypical TI.