456 research outputs found

    Topological Quantum Phase Transition in 5dd Transition Metal Oxide Na2_2IrO3_3

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    We predict a quantum phase transition from normal to topological insulators in the 5dd transition metal oxide Na2_2IrO3_3, where the transition can be driven by the change of the long-range hopping and trigonal crystal field terms. From the first-principles-derived tight-binding Hamiltonian we determine the phase boundary through the parity analysis. In addition, our first-principles calculations for Na2_2IrO3_3 model structures show that the interlayer distance can be an important parameter for the existence of a three-dimensional strong topological insulator phase. Na2_2IrO3_3 is suggested to be a candidate material which can have both a nontrivial topology of bands and strong electron correlations

    Interplay between spin-orbit coupling and van Hove singularity in the Hund's metallicity of Sr2_2RuO4_4

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    We investigate the dynamical properties of Sr2_2RuO4_4 at zero and very low temperature using density functional theory plus dynamical mean-field theory with an exact diagonalization solver. By considering rotationally invariant local interaction, we examine how Hund's coupling and spin-orbit coupling affect the correlated nature of the system. In the absence of Hund's coupling, the system shows a Fermi liquid behavior over the entire range of temperatures we consider. We confirm that the Fermi liquid persists at zero temperature even with nonzero Hund's coupling; however, at sufficient temperatures Hund's coupling significantly reduces the Fermi liquid regime and the system evolves into a typical Hund's metal. At the bare electronic occupancy of Sr2_2RuO4_4 (t2g4t_{2g}^4), a stronger Hund's metallicity accompanies a larger long-time correlator. Remarkably, electron doping further destabilizes the Fermi liquid even though the long-time correlator and magnetic fluctuations decrease upon doping. This suppression of the Fermi liquid is driven by the van Hove singularity above the Fermi level in Sr2_2RuO4_4, combined with an enhanced Van Vleck susceptibility by spin-orbit coupling. Such findings point to the important role that electronic structure plays in the behavior of Hund's metals, in addition to magnetic fluctuations.Comment: 7 pages, 4 figure

    Fundamental thickness limit of itinerant ferromagnetic SrRuO3_3 thin films

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    We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO3_3 that might arise from the orbital-selective quantum confinement effects. Experimentally, SrRuO3_3 films remain metallic even for a thickness of 2 unit cells (uc), but the Curie temperature, TC_C, starts to decrease at 4 uc and becomes zero at 2 uc. Using the Stoner model, we attributed the TC_C decrease to a decrease in the density of states (No_o). Namely, in the thin film geometry, the hybridized Ru-dyz,zx_yz,zx orbitals are terminated by top and bottom interfaces, resulting in quantum confinement and reduction of No_o.Comment: 20 pages, 4 figure

    Orbital-selective confinement effect of Ru 4d4d orbitals in SrRuO3_3 ultrathin film

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    The electronic structure of SrRuO3_3 thin film with thickness from 50 to 1 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O K-edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that orbital-selective quantum confinement effect (QCE) induces the splitting of Ru 4d4d orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition (MIT) occurring at the 4 u.c. sample. From these two clear observations we conclude that QCE gives rise to a Mott insulating phase in ultrathin SrRuO3_3 films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of RuO6_6 clusters.Comment: 7 pages, 7 figure
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