•L.H. Tjeng1,2, T. Mizokawa2,3, G.A. Sawatzky2,
G. Ghiringhelli4, O. Tjernberg4, N. B. Brookes4,
H.-J. Lin5, C.T. Chen5, S. Schuppler6,
H. Fukazawa7, S. Nakatsuji7 und Y. Maeno7,8
2Solid State Physics Laboratory, University of Groningen,
The Netherlands
3Department of Complexity Science, University of Tokyo,
Japan
4ESRF, Grenoble, France
5SRRC, Hsinchu, Taiwan
6FZK, Karlsruhe
7University of Kyoto, Japan
8CREST-Saitama, Japan
1II. Physikalisches Institut, Universität zu Köln
The nature of the phase transitions in the Ca2-xSrxRuO4 system has been studied using O 1s x-ray absorption spectroscopy. For the Mott insulator CaRuO4, we have observed that the orbital population dramatically change with temperature. Together with our finding that a substantial orbital angular momentum is present in the Ru 4d band, we argue that the cooperation between the strong spin-orbit coupling and the small distortion of the RuO6 octahedra causes the interesting changeover of the spin and orbital anisotropy as a function of temperature.
For the x = 0.09 system, we have also observed a dramatic change in the orbital occupation across the metal-insulator transition. This occupation change is discontinuous and shows a hysteresis behavior. The possible relationship between orbital occupation, magnetic interactions and effective Coulomb interactions and bandwiths will be discussed.