Electronic systems one-dimensional

Conducting Magnets Having Quasi One-Dimensional Electron System. 83... 

In this and the next sections we discuss two groups of molecule-based conducting magnets at which the %-d interaction works effectively. The first approach is the use of quasi one-dimensional electronic systems as the re-electron layers, and the other strategy is to increase the magnitude of the %-d interaction by the introduction of intermolecular halogen-halogen contacts. 

Polydiacetylenes are produced by the solid-state polymerization of single crystalline diacetylenes of the form RC=C—C=CR by 1,4-addition (see Fig. 32). The fully conjugated backbone of the polydiacetylenes is a model quasi one-dimensional electronic system being capable of representation by two extremes of bonding, sequence (a) an acetylene structure -fRC—C=C—CR)- and sequence (b) a butatriene structure -fRC=C=C=CR)-A,. There is great current debate as to the best method of representation but, in line with the belief that the nature of the side groups affect the bond lengths (and hence the... 

The considerable electrical anisotropy of this salt is made still more evident on the room-temperature polarized infrared reflection spectra [30] (see also Chapter 6 and Fig. 1 of this chapter). In addition, these reflection spectra give a remarkably clear information on the existence of strong coupling between the quasi-one-dimensional electronic system and the symmetric ag vibrational modes of the TCNQ molecules. More precisely, under the effect of this coupling, these particular modes, which are normally Raman active but infrared nonactive, acquire an anomalous intense infrared activity together with an anomalous polarization [20,30,31]. 

During the past decade there has been very intense experimental and theoretical research on the physics and chemistry of polymeric materials. This work has led to the discovery of a great number of organic and inorganic crystals built from polymers or molecular stacks which have a quasi-one-dimensional electronic system and exhibit fascinating electric, magnetic, etc. properties. Other polymers have proved to play a fundamental role in the biosciences. 

As a result of the second-order effect, also large C4, 4 2 monocycles are expected to be acetylenic as is explained by the Peierls distortion that is seen in one-dimensional electronic systems with periodic potentials [35b-e]. This effect is associated with the distortion of the potential energy surface to lower the total energy of the system through electron-phonon coupling [35b]. For a molecular system, the same effect is also referred to as the second-order Jahn Teller (SOJT) effect that leads to the vibrational-mode... 

In the process towards stable organic metals and superconductors, increasing the dimensionality could be a way to avoid the ubiquitous metal-insulator transition, which inevitably occurs in one-dimensional electronic systems. Compared with TTE and TMTSF, BEDT-TTF... 

In the case of a long chain of carbon atoms, the Jt bonds delocalize over the whole chain and form a one-dimensional electronic system. The resulting... 

Similar information can be also obtained by the ESR linewidth as a function of temperature, dominated by the Elliott mechanism through the spin-orbit coupling. It could possibly yield temperature dependence of the electrical resistivity if it were analyzed together with the g-shift and/or g-shift anisotropy and the spin dynamics data. It is noteworthy that a variety of temperature dependences are uniformly understandable with a single formulation characteristic of one-dimensional electronic systems. This mechanism is observable only in polymers with heavy nuclei, such as alkali and sulphur. It is also worth noting that the dopant nuclei could contribute to the Elliott mechanism in the donor dopant systems. Contrary to this, nuclei in the acceptor dopants could contribute little, Such a difference reflects each electronic state. Further investigation makes clear these points. 

Figure 1.1 One-dimensional electronic system with a half-filled band band structure (a) before and (b) after Peierls distortion, where E is energy and Ep is the Fermi energy...

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