Study of the Electronic Structure of the Unconventional Superconductor Sr2RuO4 by the Embedded Cluster Method
After a short account of the present state in the superconductivity (SC), the non-copper perovskite ruthenate, Sr2RuO4, superconductor is discussed. This superconductor possesses unconventional spin-triplet symmetry of Cooper’s pairs and has been a subject of intense researches. It was revealed that the substitution of Ru atoms by small amount of non-magnetic Ti atoms leads to creation of magnetic order and destruction of superconductivity. Comparative study of the electronic structure of pure and Ti-doped Sr2RuO4 was performed by the developed by our group embedded cluster method at the Hartree-Fock and MP2 electron correlation level. The representative cluster was embedded into the Madelung potential that mimic a real crystal. Accounting of interatomic interaction in our calculations leads, in contrast with the tight-binding model usually applied for study Sr2RuO4, to the large electron transfer from O to Ru. Already at the HF level the ionic model failed. At the MP2 level, the electron correlation considerably increases the electron transfer making the values of charges on atoms far enough from the charges in the formal ionic model. Calculation at the DFT level gives the similar results.
The Ti substitution induces the essential charge redistribution between d-orbitals of Ru. A drastic effect of the Ti impurity on the spin density distribution was revealed. In the Ti-substituted crystals, the local spin density near impurity disappears on Sr and localizes on Ru and four O atoms surrounding it. The NBO analysis shows that the spin density in doped crystals is localized on orbitals directed along z axis. These results are in complete agreement with experiments.
KeywordsUnconventional superconductivity Impurity effect Ruthenate Electronic correction
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