Fully Spin-Polarized, Two-Dimensional Hole and Electron Gases at the Highly Polar (111) EuTiO₃/SrTiO₃ Interface

The first experimental observation of a two-dimensional hole gas in (001) SrTiO3/LaAlO3/SrTiO3 heterostructures with carrier mobilities of ∼103 cm2/(V s) at low temperature has opened innovative avenues for future oxide electronics and demonstrated that the elimination of point defects is instrumental to achieving spontaneously confined hole carriers. Stimulated by these findings, we analyze the highly polar (111) orientation of the SrTiO3 and EuTiO3/SrTiO3 structures. Using first-principles calculations, we show that tightly confined and fully spin-polarized hole and electron gases can be realized at the p-doped and n-doped terminations of these structures, respectively. The high polarity is key to achieving strong, spontaneous carrier attraction toward the surface, provided that the macroscopic fields generated by the polarity in the interior of the material are efficiently screened out. Our findings present the (111) EuTiO3/SrTiO3 interface as a credible material for innovative spintronic applications, even capable of outperforming its (001) counterpart.