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Symmetry and the polar state of condensed molecular matter

Hulliger, Jürg ; Wüst, Thomas ; Rech, Mathias

In: Zeitschrift für Kristallographie - Crystalline Materials, 2013, vol. 228, no. 12, p. 607-610

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    Titre
    • Symmetry and the polar state of condensed molecular matter
    Auteur
    • Hulliger, Jürg. Department of Chemistry and Biochemistry, University of Berne, Freiestr. 3, 3012 Bern, Switzerland
    • Wüst, Thomas. Department of Chemistry and Biochemistry, University of Berne, Freiestr. 3, 3012 Bern, Switzerland
    • Rech, Mathias. Department of Chemistry and Biochemistry, University of Berne, Freiestr. 3, 3012 Bern, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Zeitschrift für Kristallographie - Crystalline Materials, 2013, vol. 228, no. 12, p. 607-610. OLDENBOURG WISSENSCHAFTSVERLAG
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:302322
    Summary
    Polar molecular crystals seem to contradict a quantum mechanical statement, according to which no stationary state of a system features a permanent electrical polarization. By stationary we understand here an ensemble for which thermal averaging applies. In the language of statistical mechanics we have thus to ask for the thermal expectation value of the polarization in molecular crystals. Nucleation aggregates and growing crystal surfaces can provide a single degree of freedom for polar molecules required to average the polarization. By means of group theoretical reasoning and Monte Carlo simulations we show that such systems thermalize into a bi-polar state featuring zero bulk polarity. A two domain, i.e. bipolar state is obtained because boundaries are setting up opposing effective electrical fields. Described phenomena can be understood as a process of partial ergodicity-restoring. Experimentally, a bi-polar state of molecular crystals was demonstrated using phase sensitive second harmonic generation and scanning pyroelectric microscopy