Anisotropy of the electron momentum distribution in Bi2Sr2CaCu2O8+δ superconductor studied by positron annihilation

Abstract

The temperature dependent (30 K to 300 K) Doppler broadening of the positron annihilated γ-radiation (DBPAR) measurement has been carried out on single crystalline Bi 2 Sr 2 CaCu 2 O 8+δ  (Bi-2212) high T c superconducting sample along two different crystallographic orientations. It has been observed that throughout the temperature range the electron momentum distribution has a relatively large value along the crystallographic c-axis than a-b plane. The temperature dependent DBPARL analysis shows a step like increase of S-parameter at the temperature region 92 K to116 K.

Role of defects in tailoring structural, electrical and optical properties of ZnO

“…Use of the two detectors in coincidence [143,144] help to suppress the background in measured Doppler broadened spectrum and hence the contributions of higher momentum electrons (core electrons) can be estimated [145,146]. In the present experiment, the two detector coincidence assembly has been employed here with a HPGe detector (efficiency 13%, energy resolution of 1.3 keV for the 514 keV line of 85 Sr) and a 3 00 Â 3 00 NaI (Tl) crystal coupled to a RCA 8850 photomultiplier tube placed at an angle of 180° [144]. The Doppler broadened electron-positron annihilation c-radiation (CDBEPAR) spectrum has been measured by the HPGe detector.…”

“…The CDBEPAR spectra have been recorded in a dual ADC based -multiparameter data acquisition system (MPA-3 of FAST ComTec., Germany). The CDBEPAR spectra for each sample have been analyzed by evaluating the so-called shape parameter (S-parameter) and wing parameter (W-parameter) [51,134,144]. The S-parameter, calculated as the ratio of counts in the central area of the 511 keV photo peak (|511 keV À E c | 6 0.86 keV) and the total area of the photo peak (|511 keV À E c | 6 4.25 keV), represents the fraction of positrons annihilating with the lower momentum electrons.…”

“…When one attempts to probe the increase/decrease of defects in a sample due to heat treatment or irradiation or substitution etc., usually a high quality sample (sometimes a single crystal of the same material) is taken as reference material [71]. To detect some change, if any, occurs in the defective state of a single-crystalline sample, a temperature-dependent study with reference to the results at room temperature proved to be fruitful [55,144]. To get more 6.…”

Defect driven ferromagnetism in SnO2: a combined study using density functional theory and positron annihilation spectroscopy

“…The CDBEPARL spectrum has been analyzed by evaluating the ratio curve analysis19,20 . In each CDBEPARL spectrum the S-parameter19 is calculated as the ratio of the counts in the central area of the 511 keV photo peak (| 511 keV -E γ | ≤ 0.85 keV) and the total areaof the photo peak (| 511 keV -E γ | ≤ 4.25 keV). Defects in SnO 2 were created by using 96 MeV 16 O 8+ ions from 15 UD pelletron at IUAC, New-Delhi.…”

“…It is worth mentioning that PAS spectroscopy is very much sensitive to vacancy type open volume defects in solid materials 2,6,19. .…”