Strongly-Correlated Electron Behavior and Metal-Insulator Crossover in Ru-Based Oxides with Pyrochlore-Type Structure

Abstract

The pyrochlore ruthenates Pb_2-xRE_xRu₂O_7-δ (RE = Y, Nd, Eu, Sm, Lu) have been successfully synthesized by the solid-state reaction. The solid-solution compounds of Pb_2-xRExRu₂O_7-δ show a crossover from metallic to insulating with increasing x. Owing to a localized magnetic moment on Ru site, these compounds with x > 0.2 also indicate the spin-glass like behaviors at low temperature (T < T_SG). As a result of electric resistivity measurements, the crossover was observed around x = 0.4 which is closely related to the spin-glass like behavior. In the metallic region, values of electric resistivity obey T² dependencies which indicate the strong correlation between electrons in these compounds. It is concluded that the crossover from metallic to insulating is based on the strongly-correlated electron system.