Rashba physics and superconductivity in KTaO3 2DEGs

(a) Superfluid stiffness of a KTO(111) 2DEG. (b) ARPES data and tight-binding fits (lines) of a KTO(001) 2DEG. (c-d) Zoom of the low energy region.

Just like SrTiO3, KTaO3 (KTO) is a quantum paraelectric in which oxygen vacancy doping leads to metallicity. By doping just near the surface, a 2DEG can be generated. In two recent papers we have explored further the physics of KTO 2DEGs. In a first study on (111)-oriented KTO 2DEGs we reported a gate tunable superconducting state. We extracted the superfluid stiffness of the 2-DEGs and showed that its temperature dependence is consistent with a node-less superconducting order parameter having a gap value larger than expected within a simple BCS weak-coupling limit model. The superconducting transition follows the Berezinskii-Kosterlitz-Thouless scenario, which was not reported on SrTiO3-based interfaces. 

This study was a collaboration with LPEM at ESPCI and Sapienza University of Rome.

In a second paper on KTO (001) 2DEGs, we directly visualized the Rashba-split bands using angle resolved photoemission spectroscopy. Fitting the bands with a tight-binding Hamiltonian, we extracted the effective Rashba coefficient and bring insight into the complex multiorbital nature of the band structure. Our calculations revealed unconventional spin and orbital textures, showing compensation effects from quasi-degenerate band pairs which strongly depend on in-plane anisotropy. We computed the band-resolved spin and orbital Edelstein effects, and predict interconversion efficiencies exceeding those of other oxide 2DEGs.

This work was a collaboration with Synchrotron SOLEIL and the Martin-Lüther-Universität Halle-Wittenberg.

S. Mallik, G. Ménard, G. Saïz, H. Witt, J. Lesueur, A. Gloter, L. Benfatto, M. Bibes and N. Bergeal
Superfluid stiffness of a KTaO3-based two-dimensional electron gas
Nature Comm. 13, 4625 (2022)

Sara Varotto, Annika Johansson, Börge Göbel, Luis M. Vicente-Arche, Srijani Mallik, Julien Bréhin, Raphaël Salazar, François Bertran, Patrick Le Fèvre, Nicolas Bergeal, Julien Rault, Ingrid Mertig, Manuel Bibes
Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO3 interfaces
Nature Comm. 13, 6165 (2022)