Superconductivity, cuprate temperature

All told, the theory makes predictions for weakly doped cuprates for temperatures up to Tc which are in remarkable agreement with experimentation. Our end result is that high temperature superconductivity is primarily an electron correlation effect possibly supplemented by longer range polaronic attraction of the type discussed by Mott and Alexandrov (see [8] for other references). Indeed, it can be argued that this is a theory of unbound bipolarons on a cuprate layer where the Fermion statistics are strictly maintained. 

Table 4.7 High-temperature cuprate superconducting oxides...

Cuprate high-temperature superconductors are copper-containing perovskite-derived oxides. Many of these maintain the superconducting state to temperatures above that of liquid nitrogen (Table 8.1). The stmctures of the superconductors are built up of slices of perovskite type linked by slabs with stmctures (in the main) of the rock salt (NaCl) or fluorite (CaFj) type (Section 4.6). The copper valence in most compounds lies between the formal values of Cu and Cu ". 

We have seen in the previous section that the single-layer materials exhibit substantial R-Cu exchange coupling, and they also have modest (for cuprates) superconducting transition temperatures. For the materials that contain midtiple Cu-O layers the Tc values... 

CUO2 layers appear in all cuprate superconductors and appear to be a necessary but not sufficient condition for high temperature superconduction. The La2SrCu20g 2 compound has CUO2 layers but does not superconduct. Experiments also indicate that T is proportional to the carrier density in the CUO2 layer but not to the volume carrier density, which is further evidence that the YBa2Cu202 is a two-dimensional superconductor. 

Although the high-temperature superconducting phases are formed from insulating materials by the introduction of defects, the precise relationship between dopant, structure, and properties is not fully understood yet. For example, in most of the cuprate phases it is extremely difficult to be exactly sure of the charges on the individual ions, and because of this the real defect structures are still uncertain. 

Tcr cuprates), whose superconductivity depends on subtle, phonon-free coupling between electrons. It is interesting that the highest known temperature Type-I superconductor, MgB2, shows a much larger isotope effect than does mercury (TCr (MgnB2) = 39.2 K, TCr (Mg10B2) = 40.2 K). 

Although the superconducting cuprates have high critical temperatures, their other superconducting properties such as critical currents and flux expulsion remain quite poor even after the large amount of research that has been made in this field (1). 

High temperature superconducting cuprates (HTSC) as catalysts... 

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