Superconductivity Little model

But while the BCS theory applied to low-temperature superconductivity, Little s model, after detailed calculations were carried out, had an enormously high transition temperature—typically around 2,000° K. 

The BCS and Little models for superconductivity are both based on the formation of pairs of electrons with an effective attractive interaction due to phonons or excitons respectively. Recently, J. Bardeen (8,28) revived a model, originally presented by Frohlich in 1954 (152), as a possible explanation of the reported anomalous conductivity behavior of (TTF)(TCNQ) (97). This model predates the BCS theory and relies on the direct interaction between electrons and the one-dimensional lattice resulting in the formation of charge density waves. The model has also been applied to the one-dimensional metal K2Pt(CN)4Bro.3o(H20)s (72, 457). 

As a final example, let us mention that Little 143,144) has discussed the possibility of obtaining organic superconductors that operate at high temperature. The first superconductive model compound to be proposed was a polymethine chain connected with highly polarizable sensitizing cyanine dyes (see e.g. Table 3). The first report on superconducting fluctuations in tetrathiafulvalene-tetra-cyanochinodimethane crystals appeared recently 145>. 2... 

The mechanism of superconductivity is still under investigation, but BCS theory is the currently accepted model. In short, what the model says is that the crystals line up very well in the pure material, with little to no defects present. The oxidation of copper is somewhere between +2 and +3, and that free electrons join up in the crystal and form what is known as Cooper pairs. As a pair of electrons they are less likely to scatter when they come across a defect in the crystal, and so they can travel very far and very fast. This allows the current from an outside potential to be transported with high efficiency. 

The present model for nerve impulse resembles closely the exciton mechanism of high-temperature superconductivity, as put forward by Little and Ginzburg. Little s polymer consists of a polyene spine with polarizable dye side chains, the latter forming the exciton band. Ginzburg proposes high-temperature superconductivity to be found in thin metallic films placed between highly dielectric layers. " ... 

In 1964 Little theoretically evaluated the possibility of superconductivity in polymers and suggested a model, consisting of a polyene chain with cyanine, dyelike substituents [8]. 

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