Design and Characterization of Two-Dimensional Electron Gas with Strong Spin-Orbit Coupling Based on Transition Metal Oxides

Non-technical

With the demands for faster and smaller electronics, the challenge of power dissipation, finite size effects, and several other factors places a serious limit on the future device miniaturization. Spintronics, which utilizes the electron spins instead of charges, has emerged as one of the candidates for the future generation of electronics. Traditionally, spin current is generated by using magnetic materials, which requires a magnetic field to manipulate its orientation. To significantly reduce the power consumption and incorporating multi-functionality, using an electric mean to control and manipulate spins is highly desirable. Spin Hall effect, which is due to an effect called spin-orbit coupling, can generate spin current from the charge current without using magnetic materials. This effect is characterized by spin-charge conversion efficiency which scales with the spin-orbit coupling strength in a material. Recent experiments demonstrated an unprecedented efficiency of spin-charge conversion in a two-dimensional electron gas system at a transition metal oxide interface. This project aims to develop and study new two-dimensional electron gases engineered at selected metal oxide interfaces with very large spin-orbit coupling and high mobility. The research focuses on understanding the fundamental quantum phenomena in relationship to interface engineering as well as enhancing the spin-charge conversion efficiency. The project provides scientific training for graduate and undergraduate students. The principle investigator also seeks to continue the tradition to engage in several programs specifically for recruiting and advising under-represented minority graduate students.

Technical

Rashba spin-orbit coupling is central to many emergent phenomena and has been actively explored for spintronics as it can enable the generation of spin current from a charge current through spin Hall effect. Recent demonstration of unprecedented efficiency in spin-charge conversion in a SrTiO3 based interface two-dimensional (2D) electron gas has put the oxide interfaces at the forefront for spin-orbitronics. It is believed that the combined factors of Rashba effect and high mobility has resulted in the very large effect, which exceeds that of topological insulators, even though the spin-orbit coupling strength is not large in the system. This project aims to develop high mobility and 2D confinement of the electron gases with large Rashba effect from 5d transition metal oxides with much larger spin-orbit coupling than that of SrTiO3 (3d electrons) to achieve larger spin charge conversion efficiency. Furthermore, novel magnetic and topological phases have been predicted in the (111) orientation of 5d metal oxides which will be studied. Based on the preliminary results of achieving electron gases at KTaO3 (001) based insulator interfaces, 2D electron gases with high mobility will be developed and studied in several metal oxides through materials engineering. Quantum transport measurements will be conducted at low temperature and high magnetic fields to probe the details of the band structures, Rashba splitting, and exotic phases. Spin current generation and detection using spin Hall and inverse spin Hall effect and spin diffusion length will be studied. Spin charge interconversion in oxide electron gases can work at room temperature and gate tunable, making it one of the most promising materials for spin-orbitronics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.