Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 23: Posters Superconductivity, Solids at Low Temperature

TT 23.26: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU D

Competing magnetic instabilities in 214-ruthenates — •P. Steffens¹, O. Schumann¹, O. Friedt¹, M. Braden¹, Y. Sidis², J. Kulda³, S. Nakatsuji⁴, N. Kikugawa⁴, and Y. Maeno⁴ — ¹II. Physikal. Institut, Uni Köln — ²LLB, France — ³ILL, France — ⁴Kyoto University, Japan

We present the results of inelastic neutron scattering on pure and doped Sr₂RuO₄.

The role of magnetic excitations in the pairing mechanism of the spin-triplet superconductor Sr₂RuO₄ is still unclear. The excitation spectrum is dominated by incommensurate fluctuations (caused by Fermi-surface-nesting) at q=(0.3,0.3,q_l). We determined their anisotropy of in-plane and out-of-plane component. In addition, we found a broad ferromagnetic signal (presumably the γ-band contribution) around q=0.

On minor substitution of Ru⁴⁺ by Ti⁴⁺, the incommensurate fluctuations get enhanced and finally condense into static order. We present first results on the excitation spectra of samples with and without order.

Doping with La increases the number of electrons, and the shift of the nesting signal indicates that the filling occurs predominantly in the one-dimensional bands.

Especially interesting is the phase diagram created by substitution of Sr by Ca. The compounds near Ca_1.5Sr_0.5RuO₄ show almost ferromagnetic behaviour. In contrast to Sr₂RuO₄, the excitation spectrum is dominated by fluctuations at (0.22,0,0). At low energy and temperature the spectrum becomes ferromagnetic.