Positron annihilation in high-temperature superconductors

A.A. Manuel, Positron annihilation in high-temperature superconductors 417... 

While the above-mentioned physical picture may appear too simplistic, at least at the present stage of development in the theory of superconductivity in HTSC [4], we must mention that it provides a broad qualitative framework to account for the observed temperature dependence of annihilation parameters, even in other high-temperature superconductors [39], provided the correct positron distribution within the unit cell is taken... 

Studies on other high-temperature superconductors Positron annihilation measurements across Tc, coupled with the calculations of PDD have been carried out in a variety of hole-doped superconductors that include YBa2Cu40g [48], Bi-Sr-Ca-Cu-0 [49], and Tl-Ba-Ca-Cu-0 [50, 51] systems. We will not labor with the details here, except to state that a variety of temperature dependencies are seen and these can be rationalized when the results are analysed in terms of positron density distribution and the electron-positron overlap function [39]. These calculations show that the positron s sensitivity to the superconducting transition arises primarily from the ability to probe the Cu-O network in the Cu-0 layer. The different temperature dependencies of lifetime, i.e., both the increase and decrease, can be understood in terms of a model of local electron transfer from the planar oxygen atom to the apical oxygen atom, after taking into account the correct positron density distribution within the unit cell of the cuprate superconductor. 

Positron annihilation is widely applied to study high-rc superconductors. After presenting the basic concepts (sect. 2) and discussing some experimental aspects (sect. 3), there is an overview of the results obtained so far in YBa2Cu307 (sect. 4), in YBa2Cu30y 5 with substitutions (sect. 5), and in other high-temperature superconducting oxides (sect. 6). 

---