Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.74: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Structural properties of Ca_2−xSr_xRuO₄ — •O. Schumann¹, P. Steffens¹, R. Müller¹, G. Andre², P.G. Radaelli³, P. Adelmann⁴, S. Nakatsuji⁵, Y. Maeno⁵, and M. Braden¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Laboratoire Léon Brillouin — ³ISIS Facility, Rutherford Appleton Laboratory — ⁴Forschungszentrum Karlsruhe, IFP — ⁵Department of Physics, Kyoto University

We present our x-ray- and neutron diffraction work on Ca_2−xSr_xRuO₄ which shows an astonishing rich phase diagram, even though the substitution of Sr²⁺ by Ca²⁺ is an isovalent one [1]. Pure Sr₂RuO₄ (x=2) exhibits no structural distortions. Upon Ca-doping a rotation of the RuO₆-octahedron sets in. This phase transition is strongly discontinuous, although a continuous one is allowed by symmetry. At rather higher Ca-content (x∼0.2) a metamagnetic transition is observed. The temperature and magnetic field dependence of small structural changes are an indication of an electron transfer between in- and out-of-plane t_2g-orbitals. This transfer is driven by a van-Hove singularity in one of the concerned bands [2]. At even higher Ca-content the rotational distortion changes its stacking sequence. While for x>0.2 the octahedrons in neighboring layers rotate out of phase, for x<0.2 the rotation between neighboring layers is in-phase. This rather subtle change is in coincidence with a change of the ground state properties of the samples (metallic vs. af insulating).

[1] O.Friedt et al., Phys. Rev. B 63 174432 (2001)

[2] M.Kriener et al., condmat/0408015