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CaCu3Ru4O12: a High Kondo-temperature Transition-metal Oxide
D. Takegami, C.-Y. Kuo(郭昌洋), K. Kasebayashi, J.-G. Kim, C. F. Chang, C. E. Liu, C. N. Wu, D. Kasinathan, S. G. Altendorf, K. Hoefer, F. Meneghin, A. Marino, Y. F. Liao(廖彥發), K. D. Tsuei(崔古鼎), C. T. Chen(陳建德), K.-T. Ko, A. Günther, S. G. Ebbinghaus, J. W. Seo, D. H. Lee, G. Ryu, A. C. Komarek, S. Sugano, Y. Shimakawa, A. Tanaka, T. Mizokawa, J. Kuneš, L. H. Tjeng and A. Hariki
We present a comprehensive study of 
CaCu 3 Ru 4 O 12 using bulk sensitive hard and soft x-ray spectroscopy combined with local-density approximation + dynamical mean-field theory (DMFT) calculations. Correlation effects on both the Cu and Ru ions can be observed. From the Cu 2 p core-level spectra, we deduce the presence of magnetic Cu 2 + ions hybridized with a reservoir of itinerant electrons. The strong photon energy dependence of the valence band allows us to disentangle the Ru, Cu, and O contributions and, thus, to optimize the DMFT calculations. The calculated spin and charge susceptibilities show that the transition metal oxide CaCu 3 Ru 4 O 12  must be classified as a Kondo system and that the Kondo temperature is in the range of 500–1000 K.