Polaron binding energy

These experiments yield an exciton binding energy of 0.5 eV relative to separate electron and hole. This is a large value. An important consequence, although one that is never mentioned, is that in such a case, the polaron binding energy u>p (see Fig. 7 of Chapter 11) must be larger than 0.25 eV for the absorption between polaron levels in the gap to occur below that of the exciton in practice, the polaron absorption, if it exists, will remain hidden under the excitonic absorption. 

The time needed to dress an injected free carrier with phonons (i.e., to form a polaron) is on the order of a phonon period < 1 ps. Therefore, if polaron formation occurs at all, it will be instantaneous compared to a transit time the moving charges begin their transit as polarons. In fact, if the polaron binding energy relative to the free carrier state is small [272], there is a sizable probability that the corresponding nuclear geometric... 

If one plotted piT) in an Arrhenius diagram and determined the apparent activation energy A from the tangent at a given temperature T, one would obtain A(F) = (8/9)o cr. For (t=0.1 eV and 7 =29.5 K, A=0.35eV. A is, thus, always a multiple of cr. On the other hand, since any polaron-binding energy Ep would enter the Boltzmann factor for the jump rate as p/2 in the low-field limit, the disorder contribution to A would dominate even if cr and Ep were comparable. 

We note that the reorganization energy is directly related to such quantities as the polaron binding energy = Xj2) and the dimensionless electron-phonon parameter (K-ph = N(Ep), where N(Ep) is the density of states at the Fermi level [15,23-25,43], The electron-phonon parameter is a key value in the conventional theory of superconductivity. Therefore, the results discussed before are especially relevant in the development of adequate polaron models to understand superconductivity and charge transport in organic molecular systems. 

In Ae small polaron picture, on the other hand, the electron-phonon interaction, compounded by the localization effects introduced by the disorder, leads to the formation of small polarons. The polaron binding energy is then the largest energy in the problem, and charge transport involves multiphonon-assisted hopping of small polarons (Emin, 1984). 

It is useful to note that the reorganization energy. A, is directly related to the (Holstein) polaron binding energy ( poi = A/2) [9,10] in addition, for a self-exchange reaction, the driving force AG° is zero. 

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