Circular Photogalvanic Effect in Oxide Two-Dimensional Electron Gases.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Two-dimensional electron gases (2DEGs) at the LaAlO3/SrTiO3 interface exhibit exotic phenomena like superconductivity, magnetism, and Rashba spin-orbit coupling effects.
• Despite extensive research, unexplored aspects of oxide 2DEGs remain, particularly concerning their response to light and spin polarization.

Purpose of the Study:

• To investigate and report, for the first time, the circular photogalvanic effect (CPGE) in oxide 2DEGs.
• To explore the mechanism of spin-polarized current generation and manipulation in these systems.

Main Methods:

• Selective excitation of spin-polarized electrons from SrTiO3 in-gap states to the 2DEG using circularly polarized light.
• Utilizing the spin-momentum locking mechanism, a consequence of Rashba spin-orbit coupling, to convert photoexcited carriers into electric current.
• Investigating the influence of oxygen vacancy concentration and distribution on the CPGE.

Main Results:

• Observation and characterization of the circular photogalvanic effect (CPGE) in the LaAlO3/SrTiO3 oxide 2DEG system.
• Demonstration that CPGE arises from the conversion of spin-polarized electrons, generated by circularly polarized light, into an electric current.
• Significant modification of the CPGE by controlling the density and distribution of oxygen vacancies within the SrTiO3.

Conclusions:

• The study establishes CPGE as a viable phenomenon in oxide 2DEGs, driven by Rashba spin-orbit coupling and spin-momentum locking.
• This work presents an effective method for generating and controlling spin-polarized currents in oxide heterostructures.
• The findings pave the way for novel applications in oxide spintronics, leveraging light-induced spin currents.