Metals, electron-phonon enhancement

The band structure and the DOS of the orthorhombic 3D Cgo (0-3D) polymer were calculated on the basis of the coordinates obtained by the X-ray refinement and theoretically optimized structures [68, 70, 71]. All of the calculations suggested the metallic conductivity of the 0-3D polymer with a large density of states at the Fermi level. The calculation by Yang et al. [70] suggested that the electronic band structure has steep and flat bands near the Fermi level, and possible occurrence of interband nesting which may enhance electron-phonon coupling for superconductivity. With these features it is possible that the 0-3D Cgo polymer would be a potential superconductor even without doping. The 0-3D polymer is electron... 

As described in previous works [2, 3], the o(I) below 4.2 K follows a dependence (see Eq. (3.2)) in both the parallel and the perpendicular directions to the chain axis in oriented I-(CH)x samples. The dependence indicates that the contribution from e-e interactions plays a dominant role at very low temperatures. This is also consistent with the enhanced negative contribution to magnetoconductance (MC), as explained in detail in the next section. For the intermediate temperature range (4-40 K), where inelastic electron-phonon scattering (p = 3/2) is the dominant scattering mechanism, for the parallel and the perpendicular directions to the chain axis [1131,1133]. This is also consistent with the enhanced positive contribution to MC at temperatures above 4 K. This suggests that both interaction and localization play dominant roles in o(7) at low temperatures in metallic (CH) r samples. 

Soviet scientists have been particularly interested in impurity effects in ID metals. It was shown (INV 8) that impurities in a half-filled band give a singular enhancement in the density of states at the Fermi surface. This may be another manifestation of the well known impurity localization of states in ID. This latter implies (INV 13) that at T=0, o(to)-K) as u>-K). With increasing temperature, phonons allow a hopping type transport from one localized site to another, with increasing conductivity. At still higher temperatures, phonons scatter the electrons with a corresponding decrease in a(co). The theory developed fits quantitatively with experiments on TCNQ salts with structural disorder. 

In all of the superconducting transitions observed, the superconductivity is due to the pairing of holes, as evidenced by the abrupt decrease in the thermopower from a positive value. The thermopower decreases to zero at the lower transition as expected. However, there are numerous known cases where the thermopower has the opposite sign of the carrier charge. The noble metals are a classic example. The measured thermopower has both positive and negative contributions, from holes and electrons, respectively, each of which can be enhanced by such effects as phonon drag and... 

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