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Structural and electronic properties of Sr2RuO4-Sr3Ru2O7 heterostructure

By means of first-principles calculations we study the structural and electronic properties of a superlattice made of Sr2RuO4 and Sr3Ru2O7 ruthenate oxides. Due to the symmetry mismatch of the two systems a significant structural rearrangement occurs within the superlattice. We find that at the interface the RuO6 octahedra get elongated for the Sr2RuO4 while tend to be compressed for the Sr3Ru2O7 as compared to inner layers and the bulk phases. The positions of the Sr-atoms in the Sr-O layers at the interface are strongly modified and influence the alignment of the Ru atoms with respect to the planar oxygens as well as the Ru-O-Ru in-plane bond angles. Such structural rearrangement leads to a modification of the electronic structure close to the Fermi level. The main changes occurring at the interface and in the inner layers of the heterostructure are analyzed and compared with the bulk phases of the Sr2RuO4 and Sr3Ru2O7 compounds. We show that the positions of the peaks in the density of states close to the Fermi levels get shifted and renormalized in the spectral weight. The balance between the renormalization of the bandwidth of the dxy band and that of the crystal field splitting results into a minor change of the Van Hove singularities position within the superlattice. The effective tight-binding parameters for the 4d Ru bands are determined by means of a maximally localized Wannier functions approach and used to discuss the modification of the electronic structure of the superlattice with respect to the bulk phases. Consequences on the modification of the superconducting and metamagnetic behaviour of the superlattice with respect to the bulk phases are discussed.