Positron annihilation in the high-temperature superconductorYBa2Cu3

Y. C. Jean

¹

,

S. J. Wang

²

,

Hiroshi Nakanishi

³

et al.

Anomalous Up‐and‐Down Variation of Positron Lifetime Near Tc in High‐temperature Superconductors

“…For the anomalous up-and-down variation of the mean positron lifetime, we do not suspect their actuality, because the feature was not observed in the same range of temperature in the nonsuperconducting sample and in the range of temperature of the normal state in two superconducting samples. The similar feature, although not evident as ours, observed by other authors (JEAN et al 1987;WANG et al;ZHU et al) gives also support to our results. Thus, although this anomalous feature of the positron annihilation parameters has not yet been enough considered, it is actually a very important phenomenon, and is certainly associated with some internal changes of the materials.…”

“…Among these studies the investigation on the temperature dependence of the annihilation characteristics has special attention. A decrease in the position lifetime and/or Doppler-broadened annihilation radiation line shape parameter below T, has been observed in the polycrystalline YBaCuO(123) superconductors (JEAN et al 1987(JEAN et al , 1988SMEDSKJAER et al;von STETTEN et al;SUNDAR et al 1988;USMAR et al 1987USMAR et al , 1988, in polycrystalline YBaCuO(124) , which is structurally similar to YBaCuO(l23) except for the presence of double Cu-0 chains, in the polycrystalline BiSrCaCuO (WANG et al; ZHU et al) and in TlBaCaCuO(2212 phase) ). In addition, an increase in the lifetime below T, has been observed in LaSrCuO superconductor (JEAN et al 1988), in the single crystal YBaCuO(123) sample (HARSHMAN et al), in TlBaCaCuO(2223 phase) (SUNDAR et al 1990), and CORBEL et al reported different temperature dependences on samples with different preparation conditions, and some experiments show that the positron lifetime seems to be independent of temperature in TlBaCaCuO(2201) and in BiSrCaCuO(2212) (SUNDAR et al 1988).…”

“…Since the first measurement of the positron lifetime and Doppler broadened annihilation radiation line shape parameter S across T, was performed in YBaCuO(123) by JEAN et. al.…”

State of the art simulations in electronic structure and total energy for the high temperature superconductor YBa2Cu3O7

“…The stoichiometric compound YBa 2 Cu 3 O 7 is particularly interesting from the standpoint of band theorists: it is intrinsically orthorhombic rather than (quasi) tetragonal as most HTSC are, it has two CuO 2 layers than only one which introduces additional flexibility which is peripheral to superconductivity, and it has another subsystem beside the layers (the CuO chains) which is metallic in the normal state and superconducting below T C . Furthermore, YBa 2 Cu 3 O 7 is the best experimentally studied high-T C superconductor; since clean surfaces are available in this compound so that high-resolution spectroscopic experiments can be performed and the theoretical results can be compared directly with data from angle-resolved photoemission spectroscopy [11,12], angular correlation of positron annihilation radiation [13][14][15][16][17][18], and LEED experiments [19]. The electronic band structures of YBa 2 Cu 3 O 7 and other copper oxide superconductors has been obtained by various state-of-the-art band structure calculations (reviewed by Pickett [20]), which are based on the density functional theory (DFT) in combination with the local density approximation (LDA).…”

The doping effects on the critical temperature of high-temperature superconductors

“…The difference in behaviors of electrical resistance and dc magnetization in normal and superconducting states has been considered [8] based on the Bardeen-CooperSchrieffer (BCS) theory; the electrical resistance change indicates that the volume of the vacancies decreased in the superconducting state. The electron density is much higher for the superconducting state than that for the nonsuperconduc'ting state.…”