Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 19: Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen II

TT 19.4: Vortrag

Donnerstag, 14. März 2002, 10:30–10:45, H20

Orbital excitations - a Raman scattering study on LaMnO_3+δ as function of doping — •P. Lemmens^1,2, K.-Y. Choi², G. Güntherodt², B. Büchner², V. Gnezdilov³, Yu. Pashkevich⁴, S. Barilo⁵, and S. Shiryaev⁵ — ¹IMNF, TU Braunschweig, D-38106 Braunschweig, Germany — ²2. Phys. Institut der RWTH Aachen, 52056 Aachen, Germany — ³B.I. Verkin Inst. for Low Temp. Physics NASU, 310164 Kharkov, Ukraine — ⁴A.A.Galkin Donetsk Phystech NASU, 83114 Donetsk, Ukraine — ⁵Inst. of Sol. St. and Semiconductor Physics, NAS 220072 Minsk, Belarus

Using Raman scattering experiments we investigated the excitation spectrum of untwinned LaMnO_3+δ single crystals with cation deficiency. We observe pronounced maxima of the scattering intensity for frequencies above 900cm⁻¹. The origin of the observed modes is discussed in the context of orbital excitations [1] and two-phonon scattering, as this frequency range also overlaps with the energy region of possible two-phonon processes. Doping leads to an enormous damping of these modes and a small shift to lower frequency compatible with an orbital liquid or orbital glass state. In addition phonon anomalies are induced due to a coupling to the orbital degrees of freedom. This is evidenced by the effect of a magnetic field on the orbital dynamics. We acknowledge support by DFG SPP1073, NATO and INTAS.
E. Saitoh, et al., Nature 410, 180 (2001).