Lattice relaxation, electronic screening, and spin and orbital phase diagram of LaTiO$_3$/SrTiO$_3$ superlattices

TL;DR

This paper investigates how lattice relaxation affects electronic and magnetic phases in LaTiO$_3$/SrTiO$_3$ superlattices, revealing a new orbital-ordered phase induced by structural distortions.

Contribution

It combines density functional theory and Hartree-Fock calculations to show that lattice relaxation induces a novel $xy$ orbital order not present in bulk or unrelaxed structures.

Findings

Lattice distortions of 0.1-0.2 Å in TiO$_6$ octahedra.

Significant change in Ti $d$-electron density due to screening.

Discovery of a new $xy$ orbital-ordered phase.

Abstract

The effects of lattice relaxation in LaTiO$_3$/SrTiO$_3$ superlattices are investigated using a combination of LDA$+U$ density functional theory, and Hartree-Fock effective Hamiltonian calculations. We find noticeable ($\sim 0.1$--0.2 \AA) distortions of the TiO$_6$ octahedra in the near-La region. The resulting screening changes the Ti $d$-electron density substantially. Tight-binding fits to the relaxed-lattice band structure, combined with Hartree-Fock calculations of the resulting model, reveal a novel phase with $xy$ orbital order, which does not occur in bulk LaTiO$_3$, or in the hypothetical unrelaxed structure.