Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 6: Correlated Electrons: Heavy Fermions

TT 6.2: Talk

Monday, February 25, 2008, 09:45–10:00, EB 202

Do magnetism and superconductivity coexist in CeCu₂Si₂ with 2 % and 10 % Ge doping? — •J. Arndt^1,2, O. Stockert¹, M. Deppe¹, H.S. Jeevan¹, K. Schmalzl³, A. Schneidewind^2,4, C. Geibel¹, and F. Steglich¹ — ¹MPI für Chemische Physik fester Stoffe, Dresden, Germany — ²Institut für Festkörperphysik, TU Dresden, Germany — ³Institut Laue-Langevin, Grenoble, France — ⁴FRM-II, TU München, Germany

CeCu₂Si₂, the first discovered heavy-fermion superconductor, exhibits different ground states in subtle dependence on the exact stoichiometry: It shows either incommensurate magnetic order (A), superconductivity (S), or both phenomena (A/S). Ge doping decreases the hybridisation between the localised Ce 4f and the conduction electrons, and therefore allows for studying the evolution of superconductivity in the presence of a stabilised magnetic A phase. Cu-NQR measurements on polycrystals of CeCu₂(Si_0.98Ge_0.02)₂ give indications of a coexistence of superconductivity and antiferromagnetism. We performed elastic neutron scattering on a single crystalline sample, which was mounted on a susceptibility set-up. The simultaneous recording of the susceptibility during the neutron measurement gives us the opportunity to follow the onset of superconductivity in-situ. Our results clearly indicate that, analogous to the situation in A/S CeCu₂Si₂, a phase separation between magnetic and superconducting volumes takes place, with a small magnetic volume fraction persisting down to low temperatures. These findings will be compared to results on 10 % Ge doped CeCu₂Si₂.