Observation of novel interference patterns in Bi2-xFexTe3+d by Fourier transform scanning tunneling spectroscopy

In topological insulators (TI), strong spin-orbit coupling results in non-trivial scattering processes of the surface states, whose effects include suppressed back scattering1, 2, 3, 4 weak anti-localization5, 6 and the possibility of an exotic Kondo effect that mimics graphene7. Introducing time reversal breaking perturbations and establishing long-range magnetic order has been theorized to lead to the formation of quantized magnetoelectric phenomena8, fractionalized charge excitations, and the appearance of quantum wire states9. A key, elusive, step in exploring these and other novel electronic phases is the experimental observation of charge backscattering due to spin-flip processes at the surface of a magnetically-doped TI. Here we utilize Fourier transform scanning tunneling spectroscopy (FT-STS) to probe the surface of a magnetically doped TI, Bi2-xFexTe3+d. Our measurements show the appearance of a hitherto unobserved channel of electronic backscattering along surface q-vector \Gamma\kappa. By combining FT-STS with angle-resolved photoemission data, we identify the momentum space origins of the observed q-vectors, which on comparison to a model calculation are enhanced by spin-flip scattering. Our findings present compelling evidence for the first spatial and momentum resolved measurements of magnetic impurity induced backscattering in a prototypical TI.