Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 29: New materials

HL 29.2: Vortrag

Dienstag, 26. Februar 2008, 12:15–12:30, ER 164

Orientational ordering and intermolecular interactions in the rotor-stator compounds C₆₀·C₈H₈ and C₇₀·C₈H₈ under pressure — •Komalavalli Thirunavukkuarasu¹, Chirstine A. Kuntscher¹, Gyula Bényei², István Jalsovszky², Gyöngyi Klupp³, Katalin Kamarás³, Éva Kováts³, and Sándor Pekker³ — ¹Experimentalphysik II, Universität Augsburg, D-86159 Augsburg, Germany — ²Department of Organic Chemistry, Eötvös Loránd University, P.O.Box 32, Budapest, Hungary H 1518 — ³Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences,P.O.Box 49, Budapest, Hungary H 1525

The fullerene-cubane molecular crystals C₆₀·C₈H₈ and C₇₀·C₈H₈ are the first members of the rotor-stator crystal family [1]. Static C₈H₈ molecules occupy the octahedral voids of the fullerene fcc structure and act as bearings for the rotating fullerene molecules. On cooling, C₆₀·C₈H₈ undergoes a phase transition at 140 K due to orientational ordering of the C₆₀ molecules, while C₇₀·C₈H₈ undergoes transitions at around 390 K and 150 K. A first pressure-dependent transmittance study revealed an orientational ordering transition in C₆₀·C₈H₈ induced at 0.8 GPa [2]. We have extended our spectroscopic studies to a broad frequency range for both C₆₀·C₈H₈ and C₇₀·C₈H₈ to monitor the vibrational properties and the absorption edge as a function of pressure. The nature of the observed anomalies and the electronic properties under pressure will be discussed. Supported by the DFG. [1] S. Pekker et al., Nature Materials 4, 764 (2005). [2] C. A. Kuntscher et al., Phys. Stat. Sol. (b) 243, 2981 (2006).