Role in superconductivity

It is clear that no organic compound with a polymer chain of conjugation has been found to be superconducting. It is equally clear that all known superconductors are metal, compound alloy, or metal-oxide of some kind (including ceramics ). This fact suggests that the quasi-free electrons do play an important role in superconductivity. Thus, the key to the superconductivity mechanism should lie in a combination of Covalon-conduction and quasi-free electrons. 

The e-mv couplings play an important role in superconductivity in organic materials, which contributes to static dielectric susceptibility. It is necessary to notice that not only totally symmetric modes couple with the electrons some out-of-plane molecular modes and intermolecular modes can also couple with the electron excitations. 

All the above numerical calculations were made in D=3 dimension. On the other hand it is widely known that, most of high Tc cuprates have layered structures with 2D CuO2 planes which play an essential role in the high Tc superconductivity.Therefore, it is nessesary to consider the dimensional contribution in the calculation.For this purpose,we consider the case of D = 2 + 2e (e / 0) in the post Gaussian approximation.In this case the optimal values of m and A also depend on e. Using Eq.(25) and the procedure outlined above one finds the e dependence of m2 presented in Fig.3 (solid line). 

As mentioned before, we shall use small molecules to introduce the fundamentals for more complex molecules, the real core of this book, which will be listed in the next section. Such molecules form solids with remarkable properties (metallicity, superconductivity, ferromagnetism, etc.), some of them at ambient conditions or at much lower hydrostatic pressures than those found for H2 and N2, and some technological applications have been already developed, deserving the name of functional materials. Most of the molecules studied in this book are planar, or nearly planar, which means that the synthesized materials reveal a strong 2D structural character, although the physical properties can be strongly ID, and because of this 2D distribution we shall study surfaces and interfaces in detail. In particular, interfaces play a crucial role in the intrinsic properties of crystalline molecular organic materials and Chapter 4 is devoted to them. 

This oxygen variation and the Cu oxidation states play a very important role in the superconducting behavior of this compound. For example, the oxygen content (or x vacancy), the copper oxidation states, and the onset temperatures for superconductivity are listed below for different compositions. 

In conclusion, electron microscopy techniques reveal considerable evidence for variability in composition and defect structures, such as cation and anion vacancies, extended defects, substitutional ions and oxygen interstitials these are common to all of the high temperature superconducting oxides. These defects play an important role in controlling the carrier concentrations and therefore the... 

Cu and Mn, systems that have partially filled d shells with a degenerate ground state. According to the Jahn-Teller theorem, any degenerate electronic system will spontaneously distort in such a way as to remove the degeneracy (Dunitz and Orgel 1960). The distortions around Cu " have been extensively studied and may play a role in the superconductivity found in some copper oxides (Section 13.3.2), while the distortions around Mn + play an important role in the potentially useful magnetoresistive properties of LaMnOs (Section 13.3.3). 

Thin-fiim technology has also played an important role in developing Josephson superconducting devices, which offer outstanding advantages in constructing ultrahigh-speed computers, These are tunnel-junction type devices. 

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