Physics of high temperature superconductivity

The physics underlying superconductivity is discussed. The phonon mechanism of low T-c materials is compared with the antiferromagnetic spin correlation approach to high T-c superconductivity The deformation potential theorem of Bardeen for the electron phonon coupling is extended to the electron-spin fluctuation coupling. This result shows that, for a large spin correlation length, T-c is reduced by properly pairing dressed excitations, as required by the BCS theory, instead of using bare particles as the basis for pairing, as in the present nearly antiferromagnetic fermi liquid approach. The spin bag or spin bipolaron approach circumvents these difficulties. Finally, a brief discussion of promising areas of applied superconductivity is presented.