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Metal-insulator and magnetic transition of Ca2RuO4 observed by hard x-ray photoemission spectroscopy - Yuki UTSUMI

Synchrotron SOLEIL

Bât T-18 – Parc Club Orsay – Salle de réunion

Layered perovskite Ca2RuO4 has been attracting a great interest as much as the spin triplet superconductor Sr2RuO4 because of its rich properties. Isovalent Ca substitution for Sr changes the system from superconductor to Mott insulator. Ca2RuO4 is an antiferromagnetic insulator below TN=110 K and exhibits a metal-insulator transition (MIT) at 357 K accompanied by a crystal structure distortion [1, 2]. The MIT temperature continuously decreases with increase in Sr content. For the case of Ca1.91Sr0.09RuO4, the MIT temperature becomes almost equal to TN. Despite a large number of experimental and theoretical studies, the mechanism of the MIT in Ca2RuO4 is still hotly debated. Here we report a hard x-ray photoemission spectroscopy (HAXPES) study of the electronic structure of this layered system as a function of temperature. The valence-band spectrum of Ca2RuO4 shows dramatic changes across the MIT. The valence band spectrum of Ca1.91Sr0.09RuO4 displays similar temperature evolution across the MIT. These HAXPES results indicate not only a rearrangement in t2g orbital occupation but also the importance of electronic correlations for the MIT.

[1] S. Nakatsuji et al., J. Phys. Soc. Jpn. 66, 1868 (1997)
[2] H. Fukazawa et al., Physica B 281-282, 613 (2000).


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