Dresden 2014 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 2: Optical and nonlinear optical properties, photonic
DF 2.4: Vortrag
Montag, 31. März 2014, 11:30–11:50, GER 37
Boson peak in overdoped manganites La1−xCaxMnO3 — •F. Fischgrabe1, E. Zhukova2,3,5, B Gorshunov2,3,5, V. I. Torgashev4, L. S. Kadyrov2,3, E. A. Motovilova2,3,5, T. Zhang6, R. Kremer7, U.S. Pracht5, S. Zapf5, V. V. Moshnyaga1, and M. Dressel5 — 1I. Physikalisches Institut, Universität Göttingen, Germany — 2A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Russia — 3Moscow Institute of Physics and Technology (State University), Russia — 4Faculty of Physics, Southern Federal University, Russia — 51. Physikalisches Institut, Universitat Stuttgart, Germany — 6Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, PRC — 7Max-Planck-Institut für Festkörperforschung, Germany
In the charge-ordered phase of strongly doped manganites
La1−xCaxMnO3 (x ≥ 0.5) absorption lines appear
in the terahertz spectral range for commensurate x values right below the charge-ordering temperature. They
are connected to acoustic phonons that become optically active by folding of the Brillouin zone. At lower
temperatures a strongly asymmetric extra absorption band develops at frequencies corresponding to the position
of the lowest-energy van Hove singularity in the reduced Brillouin zone. The band is assigned to the boson peak,
i.e., to the excess of lattice vibrational states over the standard Debye contribution. The folded phonons and the
boson peak do not show up for incommensurate calcium contents when no distinct Brillouin zone folding exists. Polycrystals are compared with freestanding films to determine if there are differences in the IR response.