Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 3: Correlated Electrons - Heavy Fermions

TT 3.2: Vortrag

Freitag, 4. März 2005, 10:30–10:45, TU H3027

Competition between antiferromagnetism and superconductivity in CeCu₂Si₂ — •O. Stockert¹, E. Faulhaber², N. Stüßer³, K. Prokes³, W. Schmidt⁴, G. Zwicknagl⁵, H.S. Jeevan¹, M Deppe¹, M. Loewenhaupt², C. Geibel¹, and F. Steglich¹ — ¹Max-Planck-Institut für Chem. Physik fester Stoffe, D-01187 Dresden, Germany — ²Institut für Festkörperphysik, TU Dresden, D-01062 Dresen, Germany — ³Hahn-Meitner-Institut, D-14109 Berlin, Germany — ⁴Institut Laue-Langevin, F-38042 Grenoble, France — ⁵Institut für Math. Physik, TU Braunschweig, D-38106 Braunschweig, Germany

We report on neutron scattering experiments on magnetically ordered CeCu₂Si₂ single crystals exhibiting A- and A/S-phase anomalies. Below T_N ≈ 0.8 K antiferromagnetic order has been detected with a propagation vector τ ≈ (0.215 0.215 0.53) at T = 50 mK. The magnetic order is due to nesting of the Fermi surface as indicated by renormalized band-structure calculations. The observation of incommensurate antiferromagnetic order as the nature of the A-phase in CeCu₂Si₂ suggests that a spin-density-wave instability is the origin of the quantum critical point in CeCu₂Si₂. Elastic high-resolution neutron scattering on both, A- and A/S-type crystals, reveal the long-range nature of the antiferromagnetic order in the A/S-crystal, but yield a considerable line broadening for the A-type crystal pointing to a finite domain size or correlation length. However, in energy scans no increased width of the magnetic peaks has been detected. Extensive measurements, performed on the A/S-crystal also in magnetic fields, show that in this crystal antiferromagnetism and superconductivity seem to exclude each other on a microscopic scale.