Temperature dependence of positron-annihilation parameters inYBa2Cu3

S.G. Usmar

¹

,

P. Sferlazzo

²

,

Kelvin G. Lynn

³

et al.

Theoretical Studies of the Electronic Properties of Ceramic Materials

“…24. Figure literature and thus will not be repeated,12.13 but we wish to emphasize three points: (1) Although a Fermi surface is present, there exist intrinsic hole states (4 holesicell) above the Fermi level with a significant gap separating a semiconductor-like VB and the CB.…”

“…Figure 25 shows the same band structure near the Fermi level along different symmetry lines of BZ shown in the inset. The details of these bands have been discussed widely in the published literature and thus will not be repeated,12.13 but we wish to emphasize three points: (1) Although a Fermi surface is present, there exist intrinsic hole states (4 holesicell) above the Fermi level with a significant gap separating a semiconductor-like VB and the CB.…”

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).…”

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

“…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, 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 (SUNDAR et al 1988).…”