UC Irvine

We present far infrared reflectance measurements of UBe13 and URu2Si2 down to a temperature of 2 K. At low temperatures the optical conductivity of both materials may be described in terms of free charge carriers with frequency and temperature dependent scattering rates and mass enhancements. The 'coherent regime' occurs at too low a temperature in UBe13 to be observed in our measurements, but it can be observed in URu2Si2. In addition to the behaviour of the charge carriers URu2Si2 exhibits two strong phonon lines at 109 cm-1 and 378 cm-1 and below the magnetic transition temperature there is an additional absorbtion feature near 50 cm-1. © 1988.