The Impurity Related Studies of High Tc Superconducting Materials
Rept. for 1990-1991,
LINCOLN UNIV PA DEPT OF PHYSICS
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In the superconductors of oxides, oxygen atoms play a key role of the superconductivity. From the x-ray and neutron diffraction it was known that in the orthorhombic phase the oxygens are ordered along the b axis so as to form a one dimensional Cu-O chain and a disordering of the oxygen vacancies along a axis. It is popularly agreed that the Cu-O chains play an important role in the high Tc superconductivity. The lack of the isotope effect on the superconductivity in Y-Ba-Cu-O compounds may suggest that the pairing mechanism is not a standard electron phonon interaction. According to Anderson RVB the hole amplitude drives true electron-pair amplitude via the hole-pair amplitude which has the same symmetry as a bound electron pair. If so, a sufficient concentration of Cu 3 is required. Varma et.al proposed that the charge transfer exciton Cu 3O2-yields Cu2O-is the source of the effective electron- electron attraction. And Mattheis et.al. from their band structure calculations concluded that the superconducting properties of these oxides are mainly governed by the Cu-3d and O-2p electrons. Chemical doping is one of the practical methods of confirm these proposed models, by knowing the precise locations of the impurities, and their ion structures.
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