Isotope effect in impure high-Tc superconductors

Abstract

The influence of various kinds of impurities on the isotope shift exponent α of high-temperature superconductors has been studied. In these materials the dopant impurities, like Sr in La2−xSrxCuO4, play different roles and usually occupy different sites than impurities like Zn, Fe, Ni, etc., intentionally introduced into this system to study its superconducting properties. In this paper the in-plane and out-of-plane impurities present in layered superconductors have been considered. They differently affect the superconducting transition temperature Tc. The relative change of isotope shift coefficient, however, is a universal function of Tc/Tc0 (Tc0 refers to an impurity-free system), i.e., for angle independent scattering rate and density of states function it does not depend on whether the change of Tc is due to in- or out-of-plane impurities. The role of the anisotropic impurity scattering in changing oxygen isotope coefficient of superconductors with various symmetries of the order parameter is elucidated. The comparison of the calculated and experimental dependence of α/α0, where α0 is the clean system isotope shift coefficient, on Tc/Tc0 is presented for a number of cases studied. The changes of α calculated within the stripe model of superconductivity in copper oxides reasonably well describe the data on La1.8Sr0.2Cu1−x(Fe,Ni)xO4, without any fitting parameters.

Source-reported materials — not catalogue approval

Similar papers