Superconductors, high Cooper pairs

From the quantum mechanical standpoint, the charge carriers in a superconductor are Cooper pairs with opposite momenta that result from an electron-phonon interaction that mbces the wavefunction product 0(k) 0(—k), an occupied orbital, with (k ) (—k ), which is unoccupied. This mbcing opens a band gap at the Fermi level between (/>(k) and

Cooper pairs cannot dissociate at low temperatures (below T ). High-temperature superconductors typically have a larger... 

Figure 50. The resistivity of SrO-doped l CuOj disappears at temperatures less than Tc - 40 K. The (h )2 associates (Cooper pairs) are responsible for this. The two curves are based on samples, that are annealed at differing partial pressures of oxygen.196 197 Compare here Section IV..3. (Reprinted from J. C. Philips (ed.), Physics of High Temperature Superconductors, Academie Press, New York, Copyright 1989 with permission from Elsevier.)...

The theoretical interpretation of the high temperature superconductors is still under development. The copper oxide ceramic superconductors obtain their paired conducting electrons from copper in mixed oxidation states of I and II or II and III, depending on the particular system. The paired conducting electrons are called Cooper pairs, after Leon N. Cooper. Cooper s name also gives us the C of BCS the BCS theory is an interpretation of superconductivity for low temperature superconductors (having Tc s of less than 40 K). 

The theory includes Cooper pairs of electrons but does not explain the high critical transition temperatures of the newer ceramic superconductors. 

Electrical properties of junctions formed between superconducting material, S, and a non-superconducting metallic material, N, which may be a metal or a degenerate semiconductor, are determined by special boundary conditions. If we consider a superconductor-semiconductor (S-N) interface with high transparency, a proximity effect is observed due to injection of electron pairs (Cooper pairs) from the superconductor into the semiconductor where they decay over a characteristic length, the induced coherence length. 

The Andreev reflection is the second-order quantum mechanical process by which an electron-like particle incident on a superconductor with a quasi-particle excitation energy E above the Fermi energy may be transmitted as a Cooper pair in the superconductor, if a hole-like particle (-E) is reflected along the path of the incoming electron [12], For a superconductor-semiconductor interface with low contact resistance (high transparency) and with a negligible Schottky barrier, the Andreev scattering leads to an increased conductance. 

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