Direct Observation of Broken Time-Reversal Symmetry on the Surface of a Magnetically Doped Topological Insulator

We study interference patterns of a magnetically doped topological insulator Bi2-xFexTe3+d by using Fourier transform scanning tunneling spectroscopy and observe several new scattering channels. A comparison with angle-resolved photoemission spectroscopy allows us to unambiguously ascertain the momentum-space origin of distinct dispersing channels along high-symmetry directions and identify those originating from time-reversal symmetry breaking. Our analysis also reveals that the surface state survives far above the energy where angle-resolved photoemission spectroscopy finds the onset of continuum bulk bands.