Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 32: Correlated Electrons: Poster Session

TT 32.33: Poster

Donnerstag, 28. Februar 2008, 14:00–18:00, Poster B

Orbital degree of freedom in La_7/8Sr_1/8MnO₃: Temperature-dependent rearrangement of orbital states — •Michael Merz^1,2, Christian Pinta^1,3, Sebastian Prinz², Peter Nagel¹, Andrei Samartsev^3,1, Stefan Schuppler¹, Pascal Reutler⁴, and Bernd Büchner⁴ — ¹Forschungszentrum Karlsruhe, Institut für Festkörperphysik, 76021 Karlsruhe — ²Institut für Kristallographie, Jägerstraße 17-19, RWTH Aachen, 52066 Aachen — ³Fakultät für Physik, Universität Karlsruhe, 76128 Karlsruhe — ⁴Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, 01171 Dresden

One of the most unusual phases found among charge and orbital ordered systems appears for La_7/8Sr_1/8MnO₃ below 150 K: a ferromagnetic insulating (FMI) state. With O1s near-edge x-ray absorption fine structure and single-crystal x-ray diffraction we studied the temperature-dependent evolution of this FMI phase. Our results give the following picture: Above T_JT ≈ 275 K, strong fluctuations prevent the orbitals from ordering. Upon cooling below T_JT, a first-order phase transition to a cooperative Jahn-Teller distorted phase takes place. When decreasing the temperature below 180 K, more and more O and Mn³⁺ atoms arrange their orbitals to the orbital polaron state, and this process leads to a continuous phase transition towards the FMI state. Once established, the local orbital polarons remain stable objects upon further cooling and may well form the orbital polaron lattice below T_CO as suggested by resonant x-ray scattering [1].

[1] J. Geck et al. Phys. Rev. Lett. 95, 236401 (2005).