Regensburg 2000 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 1: Schwere Fermionen

TT 1.2: Vortrag

Montag, 27. März 2000, 10:00–10:15, H20

Heavy-Fermion Behaviour in Electron Doped Cuprates — •D. Baabe¹, H.-H. Klauß¹, W. Kopmann¹, D. Mienert¹, M. Birke¹, A. Wolter¹, F.J. Litterst¹, P. Adelmann², and G. Czjzek² — ¹IMNF, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig — ²INFP, FZ Karlsruhe, Postfach 3640, 76021 Karlsruhe

Nd_2−yCe_yCuO₄ belongs to the superconducting cuprates in which the carriers of the superconducting current are electrons. In these compounds the Ce doping influences the Cu-3d magnetism by introducing charge carriers and also changes the Nd-4f spin system by diluting it. The origin of heavy-fermion behaviour - e.g. indicated by former macroscopic measurements of the specific heat and the magnetic susceptibility - is still under discussion. We want to differentiate between the proposed single ion and collective models from the viewpoint of µ⁺SR.

In 1999 we performed zero and longitudinal field µ⁺SR experiments at the PSI (Switzerland) on polycrystalline samples Nd_2−yCe_yCuO₄ with y = 0.165 and 0.18. These compounds show a large field fluctuation rate ν of about 420 MHz calculated by means of Redfield theory. This corresponds to our results for y = 0.20 however, it differs in about two orders of magnitude compared to ν in compounds with y = 0.15, measured in 1998. Surprisingly, a small increase of the charge carrier concentration from y = 0.15 to 0.165 changes the spin dynamics in this system drastically. Furthermore, we examined specimens with less Nd-Nd interactions (e.g. due to substitution of Nd by nonmagnetic Pr or Eu) which leads to similar outcomes. So in conclusion, we support the individual Nd-Cu coupling scenario proposed by e.g. P.Fulde et al.