Electronic structure and insulating nature of the (LaTiO3)(2)/(LaAlO3)(2) superlattice

Abstract

To understand the electronic structure and the role of electron correlations in a new-type Mott-insulator/band-insulator superlettice, LaTiO3/LaAlO3, we carried out first-principles calculations based on the density funcational theory within a local density approximation plus U method. In contrast to other superlattices like LaTiO3/SrTiO3 and LaAlO3/SrTiO3, the ground state electronic structure of LaTiO3/LaAlO3 was found to be insulating, which was attributed to the on-site Coulomb interactions in Ti 3d-states and to the absence of polarity discontinuity. Although the lattice relxation tended to enhance the band gap, it did not affect the main features of the electronic structures and magnetic moments. A detailed analysis revealed that the electronic structure of the (LaTiO3)2/(LaAlO3)(2) superlattice was close to a superposition of two bulk electronic states. In particular, the Ti 3d valence state maintained its Mott insulating character regardless of the lattice relaxation.