Heavy-Mass Behavior of Ordered Perovskites ACu3Ru4O12 (A = Na, Ca, La)

TL;DR

This study investigates the heavy-mass behavior in a series of ordered perovskites ACu3Ru4O12 with various A-site substitutions, revealing that electron correlations among Ru electrons, rather than Kondo effects, primarily drive mass enhancement.

Contribution

The paper provides new insights into the origin of heavy-fermion behavior in ACu3Ru4O12, emphasizing electron correlations over Kondo effects through comprehensive measurements.

Findings

Large electronic specific heat coefficients across all samples.

Wilson and Kadowaki-Woods ratios similar to heavy-fermion compounds.

Kondo effect unlikely as the main cause of mass enhancement.

Abstract

We synthesized ACu3Ru4O12 (A = Na, Na0.5Ca0.5, Ca, Ca0.5La0.5, La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200 K was observed only in CaCu3Ru4O12, suggesting the Kondo effect due to localized Cu2+ ions. However, the electronic specific heat coefficients exhibit large values not only for CaCu3Ru4O12 but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki-Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons.