Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”

TT 24.51: Poster

Mittwoch, 10. März 2004, 14:30–19:00, Poster A

Orbital-induced phonon anomalies in (La_1−yPr_y)_1−xSr_xMnO₃ and LaMnO_3+δ — •K.-Y. Choi¹, P. Lemmens^1,2, G. Güntherodt¹, Yu. Pashkevich³, V. Gnezdilov⁴, P. Reutler⁵, B. Büchner⁵, and A. Revcolevschi⁶ — ¹2. Physikalisches Institut, RWTH Aachen — ²MPI for Solid State Research, Stuttgart — ³A. A. Galkin Donetsk Phystech NASU, Ukraine — ⁴B. I. Verkin Inst. for Low Temp. Physics NASU, Ukraine — ⁵Institute for Solid State Research, IFW Dresden — ⁶Laboratoire de Physico-Chimie, Université Paris-Sud, France

We present an inelastic light scattering study of single crystalline (La_1−yPr_y)_1−xSr_xMnO₃ (0≤ x≤0.14,  y=0 and x=1/8,  0≤ y≤0.5) and LaMnO_3+δ (0.071≤ δ≤ 0.125). The studied samples range from canted antiferromagnetic insulating (CAF) to ferromagnetic insulating (FMI) phase. A giant softening up to 20 -30 cm⁻¹ of the Mn-O breathing mode around 610 cm⁻¹ is observed only for the FMI samples (0.11≤ x ≤ 0.14 and 0.085≤ δ≤0.125) upon cooling below the Curie temperature. Moreover, Pr-doping leads to the gradual suppression of the softening. This is attributed to a coupling of the breathing mode to orbital polarons, giving evidence for their presence in the FMI phase. No obvious saturation of the softening signals the instability of an orbital polaron state. In addition, the CAF samples (0≤ x≤0.1 and δ=0.071) exhibit pronounced multi-phonon features at 1000-1300 cm⁻¹. Unexpectedly, they undergo a strong softening of the peak energy and a damping as a function of temperature and doping. This odd behavior is interpreted in terms of the change of orbital forms. Work supported by DFG SPP1073