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

The discovery of a two-dimensional electron gas (2DEG) at the SrTiO₃/LaAlO₃ interface in 2004 significantly broadened the field of oxide heterostructures. It opened new possibilities for developing device concepts in electronics, quantum physics, and, more recently, spin-orbitronics by exploiting the Rashba spin-orbit coupling (SOC) that results from broken inversion symmetry at these interfaces. However, the properties required to make practical use of SOC—specifically long spin diffusion lengths and efficient spin-charge interconversion—are present in SrTiO₃-based 2DEGs only at low temperatures. In addition, the implementation of SOC-based functionality in complementary charge-based logic architectures requires two-dimensional hole gases (2DHGs). These are still largely unavailable in SrTiO₃-based systems, presenting a major limitation.

This project proposes to investigate two new classes of inversion-asymmetric polar oxide interfaces that may address these challenges: (i) BaSnO₃-based 2DEGs, which offer room-temperature mobilities more than ten times higher than SrTiO₃-based 2DEGs, and (ii) SrTiO₃- and KTaO₃-based 2DHGs. Their spin and orbital textures, as well as their transport properties, will be evaluated using tight-binding band models and Boltzmann calculations. Samples will be grown with atomic-scale precision using oxide molecular beam epitaxy. Carrier density, mobility, and Rashba SOC coefficients will be measured using magnetotransport techniques and compared to theoretical predictions.

The project will also employ three-terminal devices to modulate carrier density and systematically search for superconducting ground states. Spin-transport device structures will be fabricated to quantify spin-charge interconversion efficiency. Finally, electron- and hole-based spin-transport functionality will be combined in a single device to demonstrate three-terminal logic operation that exploits spin and charge degrees of freedom in both 2DEGs and 2DHGs.

Funded by the Deutsche Forschungsgemeinschaft (DFG) - Project number 545818886