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TT: Fachverband Tiefe Temperaturen

TT 86: Correlated Electrons: Other Materials

TT 86.8: Vortrag

Donnerstag, 3. April 2014, 11:30–11:45, BEY 81

Metal-insulator and magnetic transitions of Ca₂RuO₄ observed by hard x-ray photoemission spectroscopy — •Yuki Utsumi¹, Stefano Agrestini¹, Zhiwei Hu¹, Kyung-Tae Ko¹, Ku-Ding Tsuei², Yen-Fa Liao², Yu-Han Wu², Komarek C. Alexander¹, and Liu Hao Tjeng¹ — ¹Max-Planck Institute for Chemical Physics of Solids, Dresden, Germany — ²National Synchrotron Radiation Research Center, Hsinchu, Taiwan

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 T_N=110 K and exhibits a metal-insulator transition (MIT) at ∼357 K accompanied by a crystal structure distortion. The MIT temperature continuously decreases with increase in Sr content. For the case of Ca_1.91Sr_0.09RuO₄, the MIT temperature becomes almost equal to T_N. 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 Ca_1.91Sr_0.09RuO₄ displays similar temperature evolution across the MIT. These HAXPES results indicate not only a rearrangement in t_2g orbital occupation but also the importance of electronic correlations for the MIT.