Polarons dielectric

Throughout this book, particularly in the later chapters, we assume that a condensed electron gas can be treated as a Fermi liquid of pseudoparticles, for instance dielectric or spin polarons. We recognize that this is an unproved assumption. 

We now suppose that the carriers can form dielectric polarons, with mass enhancement up to mp, but no hopping. If so, our temperature 7i becomes T, where... 

In some of the metal-insulator transitions discussed here the use of classical percolation theory has been used to describe the results. This will be valid if the carrier cannot tunnel through the potential barriers produced by the random internal field. This may be so for very heavy particles, such as dielectric or spin polarons. A review of percolation theory is given by Kirkpatrick (1973). One expects a conductivity behaving like... 

If the concept of spin polarons as described here is correct, the most important theoretical problem at the present time is to describe the way in which they are bound together to form bosons, of dimensions about 20 A and with binding energy of the order of the Neel temperature. Any binding mechanism will certainly distort the surrounding lattice, so the cohesion may well involve dielectric or dynamic Jahn-Teller terms, subject of course to the presence of only a very small (or zero) isotope effect. 

Fig. 1. Three THz-scans at 10K The pulse transmitted through air (Efree(tJ), the unexcited sample (E,ram(t)), and the photoexcited sample ( , (/)). The 45ps delay between and E,rani is caused by the large real part of the dielectric function (see inset of Fig. 2). A less obvious phase shift also exists between E,mns and associated with the real part of e. Inset Left - the (001) face of rutile. Right - the lattice distortion when an electron is placed in the polar lattice results in polaron formation (partly) positively charged Ti-atoms are attracted, and (partly) negative O-atoms repelled (see text).

One can say that the obtained by us experimental results upon 2D exciton localization (taking place due to the growth of the crystal dielectric permeability anisotropy parameter) with o are very close to [27] where the behaviour of polaron excitons in parabolic quantum dots were considered and shown that the dot size decrease results in increasing the exciton binding energy. 

Polaron — Polarons are charged quasiparticles with spin lf. This term has been introduced by physicists as one of the possible solutions to the equations of the relevant defect model of solids in order to describe an electron in a dielectric polarizing its environment (electron-phonon coupling), electrically situated below the conduction band, and transported together with its polarized environment. Polarons and -> bipolarons are the charge carriers in oxidized or reduced (doped) -> conducting polymers. A polaron is defined as a neutral and a charged -> soliton in the same... 

The more traditional approach to treat the problem outlined by Eq. [13] goes back to the theory of polarons in dielectric crystals. It employs the two-step procedure corresponding to two traces in Eq. [13] first, the trace over the electronic subsystem is taken with the subsequent restricted trace over the nuclear coordinates. This approach, basic to the MH theory of ET, turns out to be very convenient for a general description of several quantum dynamical problems in condensed phases. It is currently widely used in steady-... 

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