Controlling electronic processes in low-dimension electron systems is centrally important for both fundamental and applied researches. While most of the previous works focused on SrTiO 3 -based two-dimensional electron gases (2DEGs), here we report on a comprehensive investigation in this regard for amorphous-LaAlO 3 / KTaO 3 2DEGs with the Fermi energy ranging from ∼13 meV to ∼488 meV. The most important observation is the dramatic variation of the Rashba spin−orbit coupling (SOC) as Fermi energy sweeps through 313 meV: The SOC effective field first jumps and then drops, leading to a cusp of ∼2.6 T. Above 313 meV, an additional species of mobile electrons emerges, with a 50-fold enhanced Hall mobility. A relationship between spin relaxation distance and the degree of band filling has been established in a wide range. It indicates that the maximal spin precession length is ∼70.1 nm and the maximal Rashba spin splitting energy is ∼30 meV. Both values are much larger than the previously reported ones. As evidenced by density functional theory calculation, these unusual phenomena are closely related to the distinct band structure of the 2DEGs composed of 5d electrons. The present work further deepens our understanding of perovskite conducting interfaces, particularly those composed of 5d transition-metal oxides.

Two-dimensional electron gas (2DEG) at the perovskite oxide interface exhibits a lot of exotic properties, presenting a promising platform for the exploration of emergent phenomena. While most of the previous works focused on SrTiO-based 2DEG, here we report on the fabrication of high-quality 2DEGs by growing an amorphous LaAlO layer on a (001)-orientated KTaO substrate, which is a 5d metal oxide with a polar surface, at a high temperature that is usually adopted for crystalline LaAlO. Metallic 2DEGs with a Hall mobility as high as ∼2150 cm/(V s) and a sheet carrier density as low as 2 × 10 cm are obtained. For the first time, the gating effect on the transport process is studied, and its influence on spin relaxation and inelastic and elastic scattering is determined. Remarkably, the spin relaxation time can be strongly tuned by a back gate. It is reduced by a factor of ∼69 while the gate voltage is swept from -25 to +100 V. The mechanism that dominates the spin relaxation is elucidated.