  The discovery of high-temperature superconductivity in Fe-based compounds
[1,2] has triggered numerous investigations on the interplay between
superconductivity and magnetism [3] and, more recently, on the enhancement of
transition temperatures through interface effects [4]. It is widely believed
that the emergence of optimal superconductivity is intimately linked to the
suppression of long-range antiferromagnetic (AFM) order, although the exact
microscopic picture of this relationship remains elusive [1] due to the lack of
data with atomic spatial resolution [5-7]. Here, we present a spin-polarized
scanning tunneling spectroscopy (SP-STS) study of ultrathin FeTe$_{1-x}$Se$_x$
(x = 0, 0.5) films grown on prototypical Bi-based bulk topological insulators.
Surprisingly, we find an energy gap at the Fermi level indicating
superconducting correlations up to Tc ~ 6 K for one unit cell thin FeTe layers
grown on Bi2Te3 substrates, in contrast to the non-superconducting FeTe bulk
compound [8]. Moreover, SP-STS reveals that the energy gap spatially coexists
with bicollinear AFM order. This finding opens novel perspectives for
theoretical studies of competing orders in Fe-based superconductors as well as
for experimental investigations of exotic phases in heterostructures of
topological insulators and superconducting layers.
