Hybridization gap versus hidden-order gap in URu2Si2 as revealed by optical spectroscopy

We present the in-plane optical reflectance measurement on single crystals of URu2Si2. The study revealed a strong temperature-dependent spectral evolution. Above 50 K, the low frequency optical conductivity is rather flat without a clear Drude-like response, indicating a very short transport lifetime of the free carriers. Well below the coherence temperature, there appears an abrupt spectral weight suppression below 400 cm−1, yielding evidence …