Direct observation of Drude behavior in the heavy-fermion UPd2Al3 by broadband microwave spectroscopy

Previous optical studies on the heavy-fermion system UPd2Al3 down to frequencies of about 1 cm(-1) (= 30 GHz) revealed a well-pronounced pseudogap at low frequencies (below 3 cm(-1)) that was attributed to magnetic correlations. Thus, the optical conductivity at even lower frequencies is of notable interest because the Drude roll-off (the high-frequency characteristic of a metal which will give information on the quasiparticle dynamics) remained hidden at extremely low frequencies. Using a novel cryogenic broadband microwave spectrometer employing the Corbino geometry we have studied the complex optical conductivity of UPd2Al3 thin films in the frequency range from 45 MHz to 20 GHz at temperatures from 1.65 to 300 K. Our spectra reveal the emergence of a strong Drude-like conductivity roll-off at frequencies of only a few GHz as the temperature is decreased (in agreement with the increase of the DC conductivity). (c) 2005 Elsevier B.V. All rights reserved.