Multiorbital structure of the two-dimensional electron gas in LaAlO_(3)/SrTiO_(3) heterostructures: the formation of a d(xy) ferromagnetic sheet

Abstract

We demonstrate the formation of a ferromagnetic two-dimensional d_(x)y electron sheet strictly confined to the TiO_(2) interface layer in LaAlO_(3)/SrTiO_(3) heterostructures. Based on first-principles density functional calculations we show that the complex subband structure of the two-dimensional electron gas (2DEG) generated at the LaO/TiO_(2) (001) interface is universal, and almost independent of the SrTiO_(3) thickness. It is composed of a ladder of d_(x)y states of light electrons and only one degenerate d_(xz,yz) heavier subband. All the states are spin polarized although the exchange splitting is only significant for the lowest energy d_(xy) subband, which leads to magnetic moments ferromagnetically coupled and localized at the interface. The SrTiO_(3) ferroelectric-like lattice distortions determine the subband occupation and therefore their orbital character, exchange splitting, and charge density profile. The complex structure of the 2DEG can explain the coexistence in the same sample of superconductivity and magnetism.