Symmetry and the polar state of condensed molecular matter
Publisher DOI
Abstract
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
Date Issued
2013
Publication Type
Article
Subject(s)
Subjects
Bi-polar state
•
Condensed molecular matter
•
Electrical polarization
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Monte Carlo simulation
•
Thermal equilibrium
•
Symmetry
Language(s)
en
Additional Credits
Journal
Zeitschrift für Kristallographie
Publisher
OLDENBOURG WISSENSCHAFTSVERLAG
ISSN
0044-2968
Access(Rights)
open.access