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Probing single-crystalline YBa2Cu3O7 across the superconducting transition temperature by positron annihilation measurements
U DE, D SANYAL, S CHAUDHURI, P M G NAMBISSAN, TH WOLF, H WÃ¼HL
Published in AMER PHYSICAL SOC
2000
Volume: 62

Issue: 21
Pages: 14519 - 14523
Abstract
Shape parameter S determined from the Doppler broadening of the positron annihilation radiation line-shape measurement (DBPARL), gives the fraction of suitably defined low momentum electrons among the annihilating electrons. Since BCS pairing in momentum space is accepted for the so-called Conventional superconductors, such studies of possible changes in the electron momentum distribution as a function of temperature across the superconducting transition in high-temperature superconductors (HTSC) may help clarify the yet unknown mechanism of superconducting pairing in HTSC. Our S vs T data at close intervals (down to 1 K) of temperature revealed one minimum at Tc in Bi-2212 pellets and two minima in the Tc region in (Bi,Pb)-2223 pellets, in addition to the somewhat better known steplike change at Tc. Similar-DBPARL·measurements presently on Y-123 single crystals show the S vs T minima in these as well as in previous (Bi,Pb)-2223 pellets to be at Tc and 0.95Tc. These observations can imply a redistribution of electron momentum similar to the better discussed charge redistribution.