At interfaces between complex oxides, electronic systems with unusual electronic properties can be generated. We report on superconductivity in the electron gas formed at the interface between two insulating dielectric perovskite oxides, LaAlO ₃ and SrTiO ₃ . The behavior of the electron gas is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The superconducting transition temperature of ≅ 200 millikelvin provides a strict upper limit to the thickness of the superconducting layer of ≅ 10 nanometers.

A two-dimensional electronic system forms at the interface between the band insulators^1,2 LaAlO₃ and SrTiO₃. Samples fabricated until now have been found to be either magnetic or superconducting, depending on growth conditions^3,4. Combining high-resolution magnetic torque magnetometry and transport measurements, we report here magnetization measurements providing direct evidence of magnetic ordering of the two-dimensional electron liquid at the interface. The magnetic ordering exists from well below the superconducting transition to up to 200 K, and is characterized by an in-plane magnetic moment. Surprisingly, despite the presence of this magnetic ordering, the interface superconducts below 120 mK. This is unusual because conventional superconductivity rarely exists in magnetically ordered metals^5,6. Our results suggest that there is either phase separation or coexistence between magnetic and superconducting states. The coexistence scenario would point to an unconventional superconducting phase as the ground state.

In 2004, Ohtomo and Hwang discovered that an electron gas is created at the interface between insulating ${\mathrm{LaAlO}}_3$ and ${\mathrm{SrTiO}}_3$ compounds. Here we show that the generation of a conducting electron gas is related to an orbital reconstruction occurring at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface. Our results are based on extensive investigations of the electronic properties and of the orbital structure of the interface using x-ray absorption spectroscopy. In particular, we find that the degeneracy of the Ti $3d$ states is fully removed and that the Ti $3d_{xy}$ levels become the first available states for conducting electrons.

Doped EuO is an attractive material for the fabrication of proof-of-concept spintronic devices. Yet for decades its use has been hindered by its instability in air and the difficulty of preparing and patterning high-quality thin films. Here, we establish EuO as the pre-eminent material for the direct integration of a carrier-concentration-matched half-metal with the long-spin-lifetime semiconductors silicon and GaN, using methods that transcend these difficulties. Andreev reflection measurements reveal that the spin polarization in doped epitaxial EuO films exceeds 90%, demonstrating that EuO is a half-metal even when highly doped. Furthermore, EuO is epitaxially integrated with silicon and GaN. These results demonstrate the high potential of EuO for spintronic devices.