Eur. Phys. J. B 25, 191-201 (2002)
https://doi.org/10.1140/epjb/e20020021

Orbital-selective Mott-insulator transition in Ca_2-xSr_xRuO₄

¹ Institute of Metal Physics, Russian Academy of Sciences-Ural Division, 620219 Yekaterinburg GSP-170, Russia
² Theoretische Physik , ETH-Hönggerberg 8093 Zürich, Switzerland
³ Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan

Corresponding author: ^a sigrist@itp.phys.ethz.ch

Received: 27 July 2001
Published online: 15 January 2002

Abstract

The electronic structures of the metallic and insulating phases of the alloy series Ca_2-xSr_xRuO₄ () are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively is an orbitally non-degenerate antiferromagnetic insulator (x=0) and a good metal (x=2). For x>0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S=1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2<x<0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees of freedom is discussed. The metal-insulator transition at x=0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal.