Coexistence of magnetic order and two-dimensional superconductivity at LaAlO3/SrTiO3 interfaces

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.