Complex variation of electron momentum distribution in (Bi,Pb)-2223 oxides across the superconducting transition

High T-c superconductors like (Bi,Pb)-2223 show an abrupt change, across T-c, in the S-parameter, calculated from Doppler broadened positron annihilation radiation lineshape (DBPARL) data. The S-parameter gives the fraction of low momentum electrons, Here we report the new feature of a sharp fall in the S-parameter on cooling the sample to its T-c (R = 0) and a subsequent complex but partial rise on further cooling. The detailed observations and possible implications are discussed.