  Mn$_{3}$Sn is a non-collinear antiferromagnet which displays a large
anomalous Hall effect at room temperature. It is believed that the principal
contribution to its anomalous Hall conductivity comes from Berry curvature.
Moreover, dc transport and photoemission experiments have confirmed that
Mn$_{3}$Sn may be an example of a time-reversal symmetry breaking Weyl
semimetal. Due to a small, but finite moment in the room temperature inverse
triangular spin structure, which allows control of the Hall current with
external field, this material has garnered much interest for next generation
memory devices and THz spintronics applications. In this work, we report a THz
range study of oriented Mn$_{3}$Sn thin films as a function of temperature. At
low frequencies we found the optical conductivity can be well described by a
single Drude oscillator. The plasma frequency is strongly suppressed in a
temperature dependent fashion as one enters the 260 K helical phase. This may
be associated with partial gapping of the Fermi surfaces that comes from
breaking translational symmetry along the c-axis. The scattering rate shows
quadratic temperature dependence below 200 K, highlighting the possible
important role of interactions in this compound.
