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H. Ishida (1) and A. Liebsch (2) (1) Nihon University, Tokyo (2) Forschungszentrum Juelich Multi-layer systems consisting of strongly correlated transition metal oxides have recently emerged as interesting artificial materials with unsual electronic and magnetic properties that might be relevant for novel devices. Charge, orbital and spin degrees of freedom associated with interfaces require theoretical descriptions that provide a layer-dependent variation between metallic and insulating properties. Dynamical mean field theory (DMFT) is used to address three topics: (1) An embedding approach is presented which permits an efficient application of DMFT to inhomogeneous strongly correlated materials. The semi-infinite substrate leads connected to the central region are represented via complex, energy-dependent embedding potentials that incorporate one-electron and many-body effects within the substrates. Results are discussed for surfaces and heterostructures of the single-band Hubbard model. In particular, the possibility of an interface Mott transition exhibiting hysteretic behavior will be explored. (2) As a result of subtle structural changes from orthorhombic to tetragonal symmetry, the interface t2g crystal field splitting of LaTiO3 in heterostructures with SrTiO3 has opposite sign. Multi- band DMFT based on finite temperature exact diagonalization (ED) then indicates that LaTiO3 is most likely a strongly correlated metal rather than a Mott insulator. The observed metallicity of this system is therefore not only due to the interface layer consisting of Ti 3d0.5 ions but due to the complete LaTiO3 film. (3) Diffusion of Sr and La ions at interfaces of LaTiO3/SrTiO3 heterostructures gives rise to effective doping. Using multi-band ED/DMFT it is shown that weak external doping of LaTiO3 causes a much larger simultaneous internal electron and hole doping of different t2g orbitals. This effect can be understood in terms of a strong doping-driven reduction of orbital polarization. (1) H. Ishida and A. Liebsch, Phys. Rev. B 79, xxx (2009) (2) H. Ishida and A. Liebsch, Phys. Rev. B 77, 115350 (2008) (3) A. Liebsch, Phys. Rev. B 77, 115115 (2008) |
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