  The unique properties of spin-polarized surface or edge states in topological
insulators (TIs) make these quantum coherent systems interesting from the point
of view of both fundamental physics and their implementation in low power
spintronic devices. Here we present such a study in TIs, through tunneling and
noise spectroscopy utilizing TI/Al$_2$O$_3$/Co tunnel junctions with bottom TI
electrodes of either Bi$_2$Te$_3$ or Bi$_2$Se$_3$. We demonstrate that features
related to the band structure of the TI materials show up in the tunneling
conductance and even more clearly through low frequency noise measurements. The
bias dependence of 1/f noise reveals peaks at specific energies corresponding
to band structure features of the TI. TI tunnel junctions could thus simplify
the study of the properties of such quantum coherent systems, that can further
lead to the manipulation of their spin-polarized properties for technological
purposes.
