Spin–orbitronics with KTaO3 two-dimensional electron gas

Srijani MALLIK

The two-dimensional electron gas (2DEG) at the interface between SrTiO3 (STO) and LaAlO3[1], displays a wide array of functionalities such as high electronic mobility, low temperature superconductivity[2] and tunable Rashba spin-orbit coupling (SOC)[3]. Among these, the Rashba SOC enables gate tunable highly efficient spin – charge interconversion which paves the path towards spin-orbitronics[4]. We have already demonstrated such effect and correlated it with band structure for STO based 2DEGs[4]. We have shown that the spin – charge conversion process is amplified by enhanced Rashba-like splitting due to orbital mixing and in the vicinity of avoided band crossings with topologically non-trivial order[4]. Further, theoretical calculation predicts that the orbital Edelstein effect exceeds the spin Edelstein effect by more than one order of magnitude in this system[5].
Similar to STO, KTaO3 (KTO) is a quantum paraelectric material that in the bulk can be turned into a metal by minute electron doping, leading to high-mobility transport[6]. Due to the presence of Ta (5d element), it is expected the Rashba SOC in KTO 2DEGs should be larger than in STO 2DEGs. In this work, 2DEGs are generated by the simple deposition of Al metal on KTO single crystals and transport measurements are performed to explore the 2DEG properties. Further, the samples are characterized by angle-resolved photoemission spectroscopy to probe the band structure, and by spin-pumping experiments to study the inverse Edelstein effect. Their spin–charge conversion efficiency is then related to the 2DEG electronic structure and compared with that of STO-based interfaces[7]. In addition, superconductivity has been observed very recently in (111) and (110) oriented KTO samples which adds further functionalities to the system. We will conclude by giving perspectives towards the implementation of KTO 2DEGs into spin-orbitronic and pure orbitronic devices.

[1] A. Ohtomo et al. Nature 2004, 427, 423
[2] N. Reyren et al. Science 2007, 317, 1196
[3] A. D. Caviglia et al. Phys. Rev. Lett. 2010, 104, 126803
[4] D. C. Vaz et al. Nature Materials 2019, 18, 1187
[5] A. Johansson et al. Phys. Rev. Research 2021, 3, 013275
[6] S. H. Wemple Phys. Rev. 1965, 137, A1575
[7] L. M. Vicente-Arche et al. Adv. Mater. 2021, 2102102