Transport properties of Ru-doped La_1.85Sr_0.15CuO₄and the effect of carrier concentration compensation

Abstract

This paper is a study of the structure and transport properties of Ru-doped La1.85Sr0.15CuO4. It is found that Ru substitution for Cu has two effects. (1) Ru doping introduces disorder into the system, which causes a metal–insulator transition with high localization. (2) There is a hole-filling effect due to the valence of the Ru ion being higher than that of the Cu ion. Increase of the strontium content could compensate for the imbalance of valence caused by doping with the high-valence Ru ion. A universal curve for Tc versus the number of holes per Cu site is observed for the La2−ySryCu1−xRuxO4 system, indicating that a rigid-band model holds and Tc correlates with features in the density of states, such as a Van Hove singularity.