IMPORTANCE OF THE MAGNETIC GROUND-STATE OF PR FOR T-C SUPPRESSION IN HIGH-T-C SUPERCONDUCTORS

An increase in the magnetic, quasi-triplet average ground-state splitt ing of Pr in Pb2Sr2Pr0.5Ca0.5Cu3O8 (T-c = 60 K) compared to that obser ved for the parent, Ca-free compound, is observed by inelastic neutron scattering. The increase in splitting due to Ca doping demonstrates t hat Ca is altering the electronic properties of Pr in addition to its role in charge transfer. It is argued that Ca doping is effectively su ppressing superconducting pair breaking by changing the single-ion mag netic properties of the Pr ions. This points toward pair breaking as t he cause of T-c suppression in Pr-based compounds.