Computational study of structural and electronic properties of superconducting La-doped SrTiO₃

Abstract

Motivated by discovery of the superconductivity in strontium titanate (SrTiO₃) doped with a smali number of electron carriers, we have carried out quantum-chemical Hartree-Fock calculations to study La-doped SrTiO₃. The crystalline lattice distortion due to the impurity presence is obtained for both cubic and tetragonal structures. The atomie movements in a region surrounding the defects show considerable differences for two crystallographic phases. La-induced local energy levels are found in the gap between the upper valence band and the conduction band. Two different States of the system, namely singlet and triplet states, are considered. These states oceur depending on how the extra electrons fili in the local energy levels. The observed electron transfer from the local energy levels to the conduction band is discussed in the light of the available experimental data on the superconductivity studies.