Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.57: Poster

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

Electronic and vibrational properties of low-dimensional perovskite-related (Sr,La)NbO_3.5−x — •C. A. Kuntscher¹, P. Haas¹, B. Gorshunov^1,2, M. Dressel¹, and F. Lichtenberg³ — ¹1. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany — ²General Physics Institute, Russian Academy of Sciences, Moscow, Russia — ³Experimentalphysik VI, EKM, Universität Augsburg, 86135 Augsburg, Germany

Polarization-dependent infrared reflectivity measurements on various (Sr,La)NbO_3.50−x single crystals [1] were carried out as a function of temperature [2]. All compounds have highly anisotropic optical properties; in particular, SrNbO_3.41 and SrNbO_3.45 show a Drude-like behavior along the chain direction and a semiconducting behavior along the perpendicular direction. In contrast, for Sr_0.8La_0.2NbO_3.50 the Drude contribution is very small, and has vanished completely for the ferroelectric insulator SrNbO_3.50. With decreasing temperature, for SrNbO_3.41 and SrNbO_3.45 a suppression of spectral weight is observed in the low-frequency optical conductivity for E∥a, with the development of a pronounced peak, which can be interpreted in terms of the opening of an energy gap of only a few meV. The gap opening most probably is due to a Peierls-type instability. In contrast, no energy gap is found for Sr_0.8La_0.2NbO_3.50, which can be related to differences in the crystal structure. Supported by the DFG.

[1] F. Lichtenberg et al., Prog. Solid State Chem. 29, 1 (2001).

[2] C. A. Kuntscher et al., to appear in Phys. Rev. B (2004).