New oxide-based two-dimensional electron and hole gases for spin-orbitronics

• Applicants: Professor Dr. Roman Engel-Herbert; Dr. Annika Johansson
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545818886

The discovery of a two-dimensional electron gas (2DEG) at the interface between SrTiO3 and LaAlO3 in 2004 immensely expanded the scope of oxide heterostructures. It laid fertile ground to develop innovative device concepts in electronics, quantum physics, and most recently spin-orbitronics by harnessing the Rashba spin-orbit coupling (SOC) arising from their built-in broken inversion symmetry. However, the desirable properties to utilize SOC effects, namely a long spin diffusion length and efficient spin-charge interconversion are present in SrTiO3 2DEGs only at low temperatures. Furthermore, utilizing SOC functionalities in charge-complementary logic architectures requires two-dimensional hole gases (2DHGs) as well, currently presenting a roadblock since SrTiO3-based 2DHGs have been largely elusive. Here, we propose to explore two new types of inversion-asymmetric polar oxide interfaces that have the potential to overcome these issues, namely (i) BaSnO3-based 2DEGs that have room temperature mobilities >10 times larger than SrTiO3 2DEGs and (ii) SrTiO3 and KTaO3-based 2D hole gases. Their spin/orbital textures and transport characteristics will be predicted from tight-binding band models and Boltzmann calculations. The samples will be grown with atomic-scale precision using oxide molecular beam epitaxy. Carrier density and mobility of the 2DEGs and 2DHGs will be determined through magnetotransport, and Rashba SOC coefficients will be experimentally quantified and compared to theory. We propose to utilize three-terminal devices to modulate carrier density and systematically search for superconducting ground states. We will fabricate spin transport device structures to quantify spin-charge interconversion efficiency. We will also combine hole- and electron-based spin transport functionalities in a single device and finally realize three-terminal logic device operation utilizing the spin and charge degree of freedom in electron and hole-based 2D gases.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Professorin Dr. Agnès Barthélémy; Professor Dr. Nicolas Bergeal