Far-infrared optical investigation of the heavy-fermion semiconductor U2Ru2Sn

We present far-infrared optical properties of the heavy-fermion semiconductor U2Ru2Sn. The optical reflectivity in the tetragonal plane shows a pronounced suppression at energies below 60meV and temperatures below 200K. These optical properties are similar to those reported for canonical heavy-fermion semiconductors. Narrow phonon-like peaks are observed at unusually high reflectivity values. We interpret the data within a temperature dependent, partial opening of a gap (or ''pseudo-gap'') in the quasi-particle excitation spectrum