A two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO${}_3$(001)

Abstract

Studies on oxide quasi-two dimensional electron gas (q2DEG) have been a playground for the discovery of novel and sometimes unexpected phenomena, like the reported magnetism at the surface and at the interface between LaAlO${}_3$ and SrTiO${}_3$ non-magnetic materials. However, magnetism in this system is weak and there are evidences of a not intrinsic origin. Here, by using in-situ high-resolution angle resolved photoemission we demonstrate that ferromagnetic EuTiO${}_3$, the magnetic counterpart of SrTiO${}_3$ in the bulk, hosts a q2DEG at its (001) surface. This is confirmed by density functional theory calculations with Hubbard U terms in the presence of oxygen divacancies in various configurations, all of them leading to a spin-polarized q2DEG related to the ferromagnetic order of Eu-4f magnetic moments. The results suggest EuTiO${}_3$(001) as a new material platform for oxide q2DEGs, characterized by broken inversion and time reversal symmetries.

Main text: 8 pages, 4 figures; Supplementary Materials: 11 pages, 11 figures