  Hanaguri et al (Science, 8th of January 2010, p. 181) have reported STM
measurements on an Fe-based superconductor Fe(Se,Te). After
Fourier-transforming their data they found three sets of sharp peaks in the
reciprocal space. They interpreted one as a Bragg peak (an umklapp scattering)
and two as resulting from quasiparticle interference (QPI) We point out that at
least one of these two peaks is also a Bragg peak, corresponding to another
reciprocal lattice vector, and therefore is not a QPI peak, and the third peak
has similar structure, too sharp for a QPI peak in a nodeless superconductor
with an isotropic gap, proposed by Hanaguri et al. We argue that this peak must
also be a Bragg peak related to a surface reconstruction doubling the unit
cell. We also calculate the QPI pattern, assuming an isotropic gap, and find
that indeed it is quite different from the experiment. Finally, we speculate
about possible origin of the magnetic field dependence of the Bragg peaks in
this compound.
