We present the in-plane optical reflectance measurement on single crystals of URu2As2. 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 life time of the free carriers. Well below the coherence temperature, there appears an abrupt spectral weight suppression below 400 cm−1, yielding evidence for the formation of a hybridization energy gap arising from the mixing of the conduction electron and narrow f-electron bands. A small part of the suppressed spectral weight was transferred to the low frequency side, leading to a narrow Drude component, while the majority of the suppressed spectral weight was transferred to the high frequency side centered near 4000 cm−1. Below the hidden order temperature, another very prominent energy gap structure was observed, which leads to the removal of a large part of the Drude component and a sharp reduction of the carrier scattering rate. The study revealed that the hybridization gap and the hidden orger gap are distinctly different: they occur at different energy scales and exhibit completely different spectral characteristics.
@article{arxiv.1203.3176,
title = {Hybridization gap versus hidden order gap in URu$_2$Si$_2$ as revealed by optical spectroscopy},
author = {W. T. Guo and Z. G. Chen and T. J. Williams and J. D. Garrett and G. M. Luke and N. L. Wang},
journal= {arXiv preprint arXiv:1203.3176},
year = {2013}
}