Nature of the Mott transition in Ca2RuO4.
We study the origin of the temperature-induced Mott transition in Ca2RuO4. As a method we use the local-density approximation+dynamical mean-field theory. We show the following. (i) The Mott transition is driven by the change in structure from long to short c-axis layered perovskite (L-Pbca→S-Pbca); it occurs together with orbital order, which follows, rather than produces, the structural transition. (ii) In the metallic L-Pbca phase the orbital polarization is ∼0. (iii) In the insulating S-Pbca phase the lower energy orbital, ∼xy, is full. (iv) The spin-flip and pair-hopping Coulomb terms reduce the effective masses in the metallic phase. Our results indicate that a similar scenario applies to Ca2-xSrxRuO4 (x≤0.2). In the metallic x≤0.5 structures electrons are progressively transferred to the xz/yz bands with increasing x; however, we find no orbital-selective Mott transition down to ∼300  K.
Gorelov
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Institut für Festkörperforschung and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany.
Karolak
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Wehling
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Lechermann
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Lichtenstein
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Pavarini
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