Exciton soliton

The soliton considered here might correspond to an atom translating in an optical held or perhaps an exciton in a solid. Under these conditions, the feedback control does not necessarily have to be ultrafast, as the propagation and velocity are at our disposal. 

T. Kobayashi In the same context, I would like to point out that, in polymer systems with degenerate ground states such as trans-polyacetylene, it may occur that a fraction of the excited species (exciton) is split into a soliton and an antisoliton with opposite charges. These can be bound by Coulombic interaction and also by steric hindrance. 

The elementary excitations of a conjugated polymer chain can be described within the mono-electronic approach as electron and hole quasiparticles [74] in a one-dimensional band structure, possibly weakly bound into extended Wannier-type excitons [71,75]. Within this framework, electron-phonon interactions lead to a peculiar family of exotic excitations including solitons, polarons, polaron pairs and bipolarons. In many cases, however, disorder is so significant that the polymer films are better described as an ensemble of relatively short conjugated segments [76], essentially behaving... 

Mobile defects are Frenkel78 excitons, Mott-Wannier excitons, polarons, bipolarons, polaritons, and solitons. 

To summarize this section, we can say that the picture of CP excitation in terms of solitons, polarons, and bipolarons is certainly incomplete, particularly when considering optical and, to a lesser extent, magnetic properties. However, there is presently no clear-cut and generally accepted picture of how and when excitons are important, although they certainly are. 

D. Solitons, polarons and polaron excitons the elementary excitations of conducting polymers... 

The soliton concept is likely to prove fruitful in many aspects of photochemistry especially where organized systems are involved, It has been proposed that charge transfer excitons in mixed-stack donor-acceptor compounds exist in a variety of solitonic states . In this effect charge transfer states couple to lattice phonons in the crystal lattice to form the comparatively stable solitons. 

The essential difference between the SWAP and the Davydov Soliton (apart from numerical matters) lies in the effect of the acoustic deformation in the former it changes the electron inter site transfer energy, whereas in the latter it changes the on site exciton vibrational energy. The difference between on site and inter site will not show up for polarons larger than the lattice spacing. 

In the original SSH model, the relaxation of the 1R state goes to a charged (S /S ) soliton pair. However, once electron correlation effect is taken into account, the negative and positive solitons appear to attract one another to form an exciton. Nevertheless, ex-... 

The operator ((, t) is the free exciton field. As a first step we are going to show that the c-number Davydov soliton ... 

A measure of the dipole-dipole interaction energy between two adjacent monomers and of the anharmonicity of the chain can be obtained by an inspection of the bandwidth of the absorption band of the monomer excitation, that forms the exciton. For a-helix proteins in which inhomogeneous broadening has been eliminated by ordering processes of the samples, the bandwidth of the C = 0 absorption at 1660 cm gives evidence of the excitonlike collectivization of the vibrational C = O excitation along the chain. This is a prerequisite for the existence of Davydov solitons on the chain. 

A powerful technique for probing the underlying physics in a material is the investigation of the behaviour of photo-excited states, which are produced by absorption of light. Electroactive conjugated polymers exhibit a wide variety of photoexcitations, such as solitons, polarons, bipolarons, and excitons. ... 

Figure 22.29 schematically shows the model originally proposed [182] for the ultrafast energy relaxation processes in PDPA films. It contains two relaxation channels [183,184] ionic, by IS and covalent, by 2Ag, which is populated following an ultrafast phonon-assisted internal conversion from the photogenerated excitons. PAg at short time is thus due to transitions from 2Ag (dark) excitons. As in long-chain polyenes [185] and f-(CH)jj [186] these excitons are subject to ultrafast recombination dynamics and this explains the ultrafast decay dynamics seen in Figure 22.28a. In degenerate ground state polymers 2Ag is unstable with respect to the formation of soliton excitations and therefore undergoes fission into two neutral SS pairs, 2Ag => 2(S° -I- S°) [18,184], followed by further separation...

Many theories have been developed (involving solitons, excitons, polarons and bipolarons) [17] to explain the conductivity phenomenon under the assumption that the chains of conductive polymers are being arranged and at least somewhat oriented in fibrils. But now, it must be explained why our dispersed (and later flocculated) polymer showed principally the same transport properties as the fibrillar conductive polymers, as can be concluded from conductivity versus temperature and thermopower measurements. 

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