Correlation-driven charge order at the interface between a Mott and a band insulator

Area of Science:

• Condensed matter physics
• Materials science
• Computational materials science

Background:

• Interfaces between complex oxides like lanthanum titanate (LaTiO3) and strontium titanate (SrTiO3) exhibit unique electronic properties.
• LaTiO3 is a Mott insulator, while SrTiO3 is a band insulator, leading to potential for novel interface phenomena.

Purpose of the Study:

• To investigate the electronic and magnetic properties of LaTiO3/SrTiO3 interfaces.
• To understand how charge and orbital ordering occurs at these interfaces under varying conditions.

Main Methods:

• Application of correlated band theory using the local density approximation with a Hubbard U correction.
• Simulation of (n, m) multilayers (1 <= n, m <= 9) with extended unit cells.

Main Results:

• Charge imbalance at the interface is accommodated by disproportionation (Ti4++Ti3+), charge ordering, and Ti3+ dxy-orbital ordering.
• Antiferromagnetic exchange coupling is observed between spins in the interface layer.
• Lattice relaxations induce conducting behavior by shifting the lower Hubbard band, but the charge and orbital order persists.

Conclusions:

• The study elucidates the mechanisms of charge and orbital ordering at LaTiO3/SrTiO3 interfaces.
• Correlated band theory effectively models the complex electronic behavior, including Mott insulating properties.
• The robustness of charge and orbital order against lattice relaxation highlights its fundamental role in interface properties.