Electron-phonon interaction static effects

At the end of this subsection it should be noted, that having a set of parameters Bpq attached to the crystallographic coordinate system one gets the opportunity (1) to describe the magnetic properties of a crystal at any appropriate value and direction of applied magnetic fields (2) to obtain reasonable estimates of different effects due to electrons phonon interaction with only those model parameters which have been introduced to describe energy spectra in the static equilibrium lattice. 

In amorphous semiconductors, electron-electron interactions are important only when two electrons of opposite spin occupy the same localized state or for Mott hopping at the Fermi level at very low temperature. Electron-phonon interactions are always present and more important in disordered than ordered semiconductors. The electron-phonon (e-p) interaction has two kinds of effects, elastic or static and... 

The success of the present model is suggestive of the existence of such universality which makes possible to draw correct results from simplified models, as the present one, which retain only the truly significant features of the disordered systems. However, even if only to check this universality, future work should include off-diagonal CPA theory (with d-orbitals in the basis set) for the electronic properties and static and dynamic effects of the electron phonon interaction for the DC conductivity and the other transport properties. 

The relevant static effects of the electron-phonon interaction are already contained in the electronic energy Eg(R) appearing in (1.7) because this energy depends on the electron-ion interaction g(R) 3is can be seen from (1.5). 

A variety of experimental techniques are available for the investigation of the electron-lattice interaction. For static phenomena such as thermal expansion and magnetostriction one can use dilatometric and X-ray techniques. For dynamic effects such as elastic constant measurements, ultrasonic propagation and phonon dispersion the methods of sound velocity and attenuation measurements, and inelastic neutron or light scattering are available. In addition high-pressure work can give valuable information for some quantities. 

The foregoing discussion leads to the conclusion that static deformations as well as phonons should be stabilized for superconducting metals by the change in effective radius associated with unsynchronized resonance of electron-pair bonds. Deformation from cubic to tetragonal symmetry, presumably the result of this interaction, has been reported for VsSi at temperatures below 21 K26- 27 and for Nb2Sn at temperatures below 43°K.28... 

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