Andri Darmawan

A two-dimensional electron gas (2DEG) forms at the interface of complex oxides like SrTi O 3 (STO) and LaTi O 3 (LTO), despite each material having a low native conductivity, as a band and a Mott insulator, respectively. The interface 2DEG hosts charge carriers with moderate charge carrier density and mobility that raised interest as a material system for applications like field-effect transistors or detectors. Of particular interest is the integration of these oxide systems in silicon technology. To this end we study the carrier dynamics in a STO/LTO/STO heterostructure epitaxially grown on Si(001) both experimentally and theoretically. Linear THz spectroscopy was performed to analyze the temperature dependent charge carrier density and mobility, which was found to be in the range of 10 12 c m − 2 and 1000 c m 2 V − 1 s − 1 , respectively. Pump-probe measurements revealed a very minor optical nonlinearity caused by hot carriers with a relaxation time of several 10 ps, even at low temperature. Density functional theory calculations with a Hubbard U term on ultrathin STO-capped LTO films on STO/Si(001) show an effective mass of 0.64–0.68 m e .

Spin-polarized two-dimensional electron gases (2DEGs) are of particular interest for functional oxide electronics applications. The redox-created 2DEG residing on the strontium titanate, SrTiO 3 (STO), side of a europium monoxide ( EuO ) / SrTiO 3 (001) interface is expected to be significantly spin polarized due to the proximity to the strong ( 7 μ B / f . u . ) Heisenberg ferromagnet EuO. We apply magnetic circular dichroism in the angular distribution (MCDAD) of photoemitted electrons to investigate whether and how the induced spin polarization of the 2DEG depends on the dimensionality of the overlaying EuO layer. The experimental data are complemented by density functional theory calculations with a Hubbard U term ( DFT + U ). We show that the EuO/STO interfacial 2DEG is spin polarized even for ultrathin EuO overlayers, starting at an EuO threshold thickness of only two monolayers. Additional EuO monolayers even increase the induced magnetic Ti moment and thus the spin polarization of the 2DEG. Our results and the potential to enhance the magnetic order of EuO by other proximity effects indicate that the EuO/STO(001) interface is an ideal template for creating (multi-)functional spin-polarized 2DEGs for application in oxide electronics. Published by the American Physical Society 2025