Our recent measurements of positron lifetime (related to electron density at the annihilating sites) components or τi and Doppler broadening of positron annihilation radiation lineshape or S-parameter (denoting the fraction of low-momentum electrons among the annihilating electrons) on Bi-2212 and (Bi,Pb)-2223 pellets and Y-123 single crystals firstly confirm step-like changes across Tc. Our second and new observation is that S versus T graph in the superconducting transition region shows a double minimum for 2223 and 123 and a single minimum for 2212. These steps and minima, not seen for superconductors like Nb3Sn, are linked to such features of HTSC electronic structure as are not found in conventional superconductors.

D SANYAL

P M G NAMBISSAN

TH WOLF

U DE

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

&nbsp;

The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

&nbsp;

It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Unconventional features of oxide HTSC from positron annihilation measurements

Physica B: Condensed Matter

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.

Physical Review B - Condensed Matter and Materials Physics

Probing single-crystalline YBa2Cu3O7 across the superconducting transition temperature by positron annihilation measurements

The present measurement of positron annihilation lifetimes for the high-(Formula presented) superconductor (Formula presented) or (Bi, Pb)-2223, as a function of temperature, has been inspired by our recent DBPARL (Doppler-broadened positron annihilation radiation line shape) finding of a step and minima in the region around (Formula presented) K, in the variation with temperature, of the fraction of low momentum electrons at the annihilation sites. The positron annihilation lifetime in the superconductor probes the number density of electrons at the annihilation sites. The present work observes a reduction of lifetime components in the (Formula presented) region. Significant changes in the lifetime components in other temperature regions have also been observed and discussed. © 1998 The American Physical Society.

Probing superconductors from 30 to 300 K by positron-lifetime measurements

For single-phase Bi-2212, Doppler broadened positron annihilation radiation line shape (DBPARL) parameter S has been measured from 15 to 300 K. S represents the fraction of low momentum electrons involved in the annihilation process. It shows a broad dip in S over 58 to 90 K in contrast to the 90-110 K complex dip in (Bi, Pb)-2223. The shift of the dip to lower temperatute for the lower-Tc superconductor proves that our observed decrease of the fraction of low momentum electrons in the Tc-region is linked to superconducting pairing.

Electron momentum re-distribution due to superconducting transition in Bi-2212 and (Bi, Pb)-2223 oxides

High Tc superconductors like (Bi,Pb)-2223 show an abrupt change, across Tc, 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 Tc (R = 0) and a subsequent complex but partial rise on further cooling. The detailed observations and possible implications are discussed.

Journal	Data powered by TypesetPhysica B: Condensed Matter
Publisher	Data powered by TypesetElsevier Science Publishers B.V., Amsterdam
ISSN	0921-4526