Abstract
We measured the polarized optical conductivity of from room temperature down to 5 K, covering the Kondo state, the coherent Kondo liquid regime, and the hidden-order phase. The normal state is characterized by an anisotropic behavior between the plane and -axis responses. The -plane optical conductivity is strongly influenced by the formation of the coherent Kondo liquid: a sharp Drude peak develops and a hybridization gap at 12 meV leads to a spectral weight transfer to mid-infrared energies. The -axis conductivity has a different behavior: the Drude peak already exists at 300 K and no particular anomaly or gap signature appears in the coherent Kondo liquid regime. When entering the hidden-order state, both polarizations see a dramatic decrease in the Drude spectral weight and scattering rate, compatible with a loss of about 50% of the carriers at the Fermi level. At the same time a density-wave-like gap appears along both polarizations at about 6.5 meV at 5 K. This gap closes respecting a mean-field thermal evolution in the plane. Along the axis it remains roughly constant and it “fills up” rather than closing.
- Received 17 June 2015
- Revised 10 July 2015
DOI:https://doi.org/10.1103/PhysRevB.92.045129
©2015 American Physical Society