A Spin-polarized two dimensional electron gas at the EuTiO$_{3}$(001) surface

The discovery of a surface/interfacial quasi 2-dimensional electron gas (q2DEG) in SrTiO$_{3}$ boosted expectations for novel oxide electronics due the intriguing and rich physics uncovered, including multiband and possibly unconventional superconductivity, large Rashba-like spin-orbit coupling and large spin to charge conversion efficiency. While magnetic effects have been reported, several studies attributed them to weak-(para)magnetism induced by extrinsic defects, such as oxygen vacancies. Here, by using in-situ high-resolution angle resolved photoemission we demonstrate that EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$, hosts a q2DEG at its (001) surface characterized by distinctive features reproduced by ab-initio calculations. In particular, we find that the exchange coupling between localized and delocalized Ti 3d electrons and magnetic Eu 4f states favors a robust ferromagnetic ground state. The results establish EuTiO3 as a new material platform for spin-polarized oxide q2DEGs.