PAIR-BREAKING, INTRINSIC T-C, AND THE UPPER LIMIT OF T-C IN THE CUPRATES

The presence of magnetic impurities leads to a drastic decrease in T-c in the overdoped region, gaplessness, and the usual temperature depen dence of H-c2. The magnetic moments are localized on the apical oxygen site, and this allows us to explain the increase in T-c with the incr ease in the number of Cu-O planes in the unit cell. Applied pressure c an raise T-c above the usual value at optimum doping, toward the ''int rinsic'' T-c. The cuprates as a class of compounds have an upper limit of T-c in the range T-c,T-upp = 160-170 K.