Abstract:
Temperature dependent resistivity, p, magnetic susceptibility, X, and far-infrared reflectance
measurements were made on the low Tc superconductor UBe13. Two variants
of UBe13 have been proposed, named 'L'- (for low Tc ) and 'H'-type (for high Tc ). Low
temperature resistivity measurements confirmed that our sample was of H-type and that
the transition temperature was at 0.9 K. This was further confirmed with the observation
of this transition in the AC-susceptibility. Low temperature reflectance measurements
showed a decrease in the reflectivity as the temperature is lowered from 300 to 10 K,
which is in qualitative agreement with the increasing resistivity in this temperature range
as temperature is lowered. No dramatic change in the reflectivity was observed between
10 and 0.75 K. A further decrease of the reflectance was observed for the temperature
of 0.5 K. The calculated optical conductivity shows a broad minimum near 80 cm-1
below 45 K. Above 45 K the conductivity is relatively featureless. As the temperature
is lowered, the optical conductivity decreases. The frequency dependent scattering rate
was found to be flat for temperatures between 300 and 45 K. The development of a
peak, at around 70 cm-1 was found for temperatures of 45 K and below. This peak has
been associated with the energy at which the transition to a coherent state occurs from
single impurity scattering in other heavy fermion systems. The frequency dependent
mass enhancement coefficient was found to increase at low frequencies as the frequency
decreases. Its' magnitude as frequency approaches zero also increased as the temperature
decreased.
