With recent developments in the field of spin-orbitronics, two-dimensional electron gases (2DEGs) with Rashba-type spin-orbit coupling have emerged as an important component of spin-based devices. One of the promising platforms is the 2DEG in SrTiO3-based structures, which has been the fundamental building block of oxide electronics. The 2DEG formed due to the redox reactions at metal/SrTiO3 interfaces has been incorporated into magnetic heterostructures, demonstrating efficient spin-to-charge conversion through the inverse Edelstein effect due to the sizable Rashba spin-orbit coupling. However, evidence for the charge-to-spin conversion, a technologically more important process, has been lacking, and furthermore, the spin transport mechanism in the magnetic heterostructure has been unclear. Here, the charge-to-spin conversion induced by the direct Edelstein effect in the 2DEG at an Al/SrTiO3 interface is demonstrated. The effective charge-to-spin conversion efficiency of the 2DEG exceeds 10% at room temperature, which is comparable to that of the archetypal spin-to-charge converter, Pt. The high effective charge-to-spin conversion efficiency is found to be suppressed by decreasing temperature, demonstrating a crossover of the dominant spin transport mechanism from the inelastic tunneling to elastic tunneling induced by decreasing temperature. These findings will provide a clue to unlock the full potential of oxide-based spin-orbitronic devices.
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