Anomalous fermi liquid state in pyrochlore heavy electron superconductor Cd2Re2O7

Cd2Re2O7 is a pyrochlore superconductor with a transition temperature Tc near 2 K. We report on the electronic background of Cd2Re2O7 at temperatures above and below Tc as determined from the far-infrared optical properties. In the normal state at low temperatures and frequencies, Cd2Re2O7 behaves as a mass enhanced Fermi liquid. Comparing the coefficients of the quadratic frequency and temperature dependence of the optical- and dc-resistivities leads to the conclusion that Cd2Re2O7 is an anomalous Fermi liquid with contributions to the scattering from elastic processes. In the superconducting state the elastic scattering is found to be somewhat reduced. We also find evidence for a weak pseudogap-like feature which may be due to the hybridization of the localized and itinerant-electron states. The superconducting state magnetic penetration depth extracted from the imaginary part of the optical conductivity is a relatively large value of λ(T=0.5K)≈6200Å.