Growth optimization, spin, and quantum phenomena in high-mobility γ-Al₂O₃/SrTiO₃ interfaces: Towards spin-charge conversion

During the last 2-3 centuries, electronic properties of materials have been intensely studied. These studies have yielded important technologies ranging from energy storage to data processing.[2, 35, 79]
One peripheral subject remain relatively unexploited, albeit expected to have a huge potential: Spintronics. Spintronics, the study and utilization of electron spin, is predicted to allow the invention of alternatives to implemented electronics with higher energy efficiency and logically denser properties.[37, 59]
Perovskite titanates have shown many properties relevant for investigating spintronics, with SrTiO₃ being one of the most explored.[11] In 2004 the discovery of the 2-dimensional electron gas between LaAlO₃ and SrTiO₃ [69], activated the interest from the scientific community considerably. This interest resulted in the discovery of an interface between γ-Al₂O₃ and SrTiO₃ showing high carrier mobilities and indications of 2-dimensionality.[17] Such a 2-dimensional high-mobility interface is highly relevant for spintronics.
This thesis first outline the background theory and experimental techniques necessary to understand the experiments conducted during the PhD project. Then relevant literature about oxide interfaces, with additional focus on LaAlO₃/SrTiO₃ and γ-Al₂O₃/SrTiO₃, is reviewed. Subsequently, the growth and structural characterization of the γ-Al₂O₃/SrTiO₃ interfaces measured during the PhD project is presented,
showing signs of high carrier mobilities, epitaxial, and crystalline growth. Then low-temperature (20 mK < T < 300 K) measurements are exhibited, showing properties resembling superconducting, spin-scattering, transport through 2 electronic bands, high carrier densities and high carrier mobility. Following low-temperature, measurements on high-mobility γ-Al₂O₃/SrTiO₃ in a pulsed high magnetic field (B ≤ 60 T) conducted in Los Alamos National High Magnetic Field Laboratory are presented indicating a correction to the E-k-dispersion with Zeeman effect. Then, at the time of thesis submission, recent experiments of anisotropic magnetoresistance are displayed. At last, based on the work described in this thesis, it is concluded that high-mobility γ-Al₂O₃/SrTiO₃ is likely formed through electron-donating oxygen vacancies, hosts unpaired spins near the interface, shows superconductivity with Josephson Junction dynamics at temperatures T_C ≈ 100 mK, transmits electrons through a superposition of 2D and 3D transport, show indications of correction in the E-k-dispersion with Zeeman effect, and have a non-negligible Rashba Spin-Orbit coupling. This paves the way for spin-charge interconversion through Rashba-Edelstein Effect, that takes place in 2-dimensional Rashba materials with an efficiency λ ∝ μα_R, with carrier mobility, μ, and Rashba spin-orbit coupling, α_R.[28, 59]