Tunable spin polarization and superconductivity in engineered oxide interfaces

Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials’ engineering tool in today’s semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO 3 at the interface between LaAlO 3 and SrTiO 3 oxides 1,2 . Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO 3 layer ( TFM = 6–8 K) and is due to the exchange interaction between the magnetic moments of Eu-4 f and of Ti-3 d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin–orbit coupling in the same q2DES makes the LaAlO 3 /EuTiO 3 /SrTiO 3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.