CESR in superconductors: Relevance of highT c copper oxide systems

CESR is a highly effective tool to study the interaction among conduction electrons in normal metals. In superconductors belowT _c it can reveal vital information concerning the pairing interactions. A comparative study of highT _c and conventional superconductors is presented and it is shown that the disappearance of CESR in the superconducting state is a feature common to both conventional and highT _c superconductors and establishes the importance of exchange interactions in pairing. This is supported by experimental observations.