Electron-lattice interactions, organic materials

Here, Hz is the Zeeman term, Hq is the quadrupolar interaction term for nuclei with 1 1, Hd is the dipolar interaction term for nuclei with 1 = 1/2, Hs is the electron shielding term and Hj is the J-coupling term. Spin relaxations will be induced by the time fluctuations of these interaction terms. For example, H spin-lattice relaxation behaviour is dominated by Hq, whereas Hq mainly determines the relaxation process of the H or magnetization in organic materials. In some cases without significant contributions from Hq and Hq, the time fluctuations of Hs and Hj also induce spin relaxation for example, the magnetization of a carbonyl carbon with a large chemical shift anisotropy relaxes due to the contribution from the time fluctuation of Hs. Nevertheless, since the main interest of polymer scientists is NMR, we focus on the description of the relaxation process in this chapter. 

Superconductivity was first discovered in mercury by H. Kamerlingh Onnes in 1911 (329) and eluded attempts at explanation until, in 1957, Bardeen, Cooper, and Schrieffer formulated the BCS theory (29) based on an electron-lattice-electron interaction. This theory and two others [by W. A. Little (268) and H. Frohlich (152)] are briefly described a full review is beyond the scope of this article. Interest in this area has been heightened by the report of superconducting fluctuations in the one-dimensional organic material, tetrathio-fulvalenium tetracyanoquinodimethanide, (TTF)(TCNQ) (97). 

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