Relaxation-time enhancement in the heavy-fermion systems CePd/sub 3/ and UPt/sub 3/
The frequency dependence of the electrical conductivity was measured at microwave- and millimeter-wave frequencies in the heavy-fermion materials CePd/sub 3/ and UPt/sub 3/. Although the conductivity is independent of the frequency at high temperatures, a substantial deviation from the dc conductivity develops in the low-temperature, ''coherent'' regime. The observed dependence on frequency agrees with a Drude expression sigma/sub 1/(..omega..) = sigma/sub d//sub c//(1+..omega../sup 2/tau/sup *//sup 2/), incorporating a renormalized relaxation time tau/sup */ typically around 10/sup -12/ s. From tau/sup */ and the measured sigma/sub dc/, the renormalized plasma frequency, ..omega../sub p//sup */ = (sigma/sub d//sub c//epsilon/sub 0/tau/sup */)/sup 1/2/ is evaluated. By comparison of ..omega../sub p//sup */ with the plasma frequency obtained at optical frequencies, where renormalization effects do not occur, an enhanced mass is extracted. Similar results are found by comparison of ..omega../sub p//sup */ with the linear specific-heat coefficient. The enhanced relaxation time is approximately given by the expression tau/sup *//tau = m/sup *//m/sub e/, where tau and m/sub e/ refer to the unrenormalized quantities, supporting the conjectures of Varma and Fukuyama, and the theoretical models advanced by Millis and co-workers, Auerbach and co-workers, and Coleman. An internally consistent analysis of sigma(..omega..) in terms of an enhanced relaxation time also suggests that a frequency-dependent density of states does not play a dominant role in the frequency-dependent response measured in the millimeter-wave spectral range.
- Research Organization:
- Department of Physics and Solid State Science Center, University of California, Los Angeles, California 90024
- OSTI ID:
- 6485239
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Vol. 39:4
- Country of Publication:
- United States
- Language:
- English
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360104* - Metals & Alloys- Physical Properties