Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 3: Schwere Fermionen, Kondo-Systeme I

TT 3.2: Vortrag

Montag, 11. März 2002, 09:45–10:00, H18

The Nature of Heavy Quasiparticles in Magnetically Ordered Heavy Fermions — •M. Dressel¹, B. Gorshunov¹, N. Kasper¹, G. Grüner², M. Huth³, and H. Adrian³ — ¹1. Physikalisches Institut, Universität Stuttgart — ²Department of Physics, University of California, Los Angeles — ³Physikalisches Institut, Universität Mainz

We have determined the frequency dependence of the effective mass of uranium-based heavy fermions UPd₂Al₃ and UPt₃ by optical experiments in the frequency range from 10 GHz to 1.2 THz (0.04 meV to 5 meV). Besides the hybridization gap opens around 10 meV, a well pronounced pseudogap of approximately 0.2 meV develops in the optical response of UPd₂Al₃; we relate this to the antiferromagnetic ordering. In addition we observe a narrow zero-frequency conductivity peak less than 1 cm⁻¹ wide, which contains only a fraction of the delocalized carriers. The analysis of the spectral weight infers a loss of kinetic energy associated with the superconducting transition in UPd₂Al₃. From the frequency dependent mass and scattering rate for UPd₂Al₃ and UPt₃ we derive the energies essential for the heavy quasiparticle and find that the enhancement of the mass mainly occurs below the energy which is related to magnetic correlations between the local magnetic moments and the itinerant electrons. This implies that the magnetic order in these compounds is the pre-requisite to the formation of the heavy quasiparticle and eventually of superconductivity.