| 概 要 |
Ferroelectricity is a demanded effect in fundamental and applied solid state physics. We discuss a feasibility of obtaining ferroelectric, and the same time electronically and optically active, carbon-based materials: conducting polymers and may be graphene ribbons. Ferroelectricity related to the charge ordering was discovered in quasi-1D organic conducting crystals (TMTTF)2X (Grenoble-Orsay, France, 2001), and now is intensively studied, with new impacts from nonlinear optics, in layered BEDT based compounds (IMS, Japan).
The interpretation was endorsed by understanding of the combined Peierls effect in conducting polymers (N.K.&S.B. 1981). In analogy with other classes of new ferroelectric materials (Tokura et al, 1989-2010), the microscopic picture is based on two coexisting symmetry lowering effects:
dimerizations of bonds and of sites: one of them being build-in, another comes as a spontaneous symmetry breaking. For ribbons of graphenes, the zigzag edges possess the build-in dimerization of sites, while the spontaneous one may come from the guessed lattice reconstruction. For polymers, we argue that a prototype polymer has been already synthesized (Kyoto-Osaka, Japan) and studied for nonlinear optics (Utah, US). But still it is waiting to be tested for signatures of the ferroelectricity. The physics of expected solitons may allow for manipulating the visible-range optics by transient ferroelectric processes, and vice versa. We shall also discuss unresolved problems of optics in the CO state of quasi-1D organic conductors.
N. Kirova, S. Brazovskii, Physica B, 404, 382 (2009). If the time allows, Prof. Serguei Brazovskii may informally add on unresolved issues in quasi 1D organic compounds.
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