Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO3 interfaces

Abstract

Rashba interfaces have emerged as promising platforms for spin-charge interconversion through the direct and inverse Edelstein effects. Notably, oxide-based two-dimensional electron gases display a large and gate-tunable conversion efficiency, as determined by transport measurements. However, a direct visualization of the Rashba-split bands in oxide two-dimensional electron gases is lacking, which hampers an advanced understanding of their rich spin-orbit physics. Here, we investigate KTaO3 two-dimensional electron gases and evidence their Rashba-split bands using angle resolved photoemission spectroscopy. Fitting the bands with a tight-binding Hamiltonian, we extract the effective Rashba coefficient and bring insight into the complex multiorbital nature of the band structure. Our calculations reveal unconventional spin and orbital textures, showing compensation effects from quasi-degenerate band pairs which strongly depend on in-plane anisotropy. We compute the band-resolved spin and orbital Edelstein effects, and predict interconversion efficiencies exceeding those of other oxide two-dimensional electron gases. Finally, we suggest design rules for Rashba systems to optimize spin-charge interconversion performance.

Anisotropic Rashba coupling to polar modes in KTaO3

“…It is already interesting that the Rashba-like coupling to the polar modes we presented here in the higher cubic symmetry of the bulk is intrinsically anisotropic. In heterostructures there will be additional crystallographic orientation dependent strong crystal field effects [5,30,31] affecting both the electrons and their interaction with the polar modes. This calls for ab initio computations in relevant slab geometries [32], including appropriate electrostatic boundary conditions [33], to directly address the crystallographic orientation dependence of the Rashba interaction in heterostructures following the approach we presented here.…”

Light‐Induced Giant Rashba Spin–Orbit Coupling at Superconducting KTaO3(110) Heterointerfaces

“…The highest Rashba coefficient is similar to the significant spin splitting of band structure with α R = 0.32 eVÅ extracted from the angle‐resolved photoemission spectroscopy (ARPES) in (001). [ 56 ] (The corresponding Δ so are in Figure S10, Supporting Information. )…”

“…b) The α R and E so as a function of carrier density. c) Comparative graph of Rashba coefficients mainly extracted from the transport measurements of various mainstream 2DESs for low‐power spintronics, including KTO‐based systems (Al/KTaO 3 with g ‐factor of 0.5–2, [ 48 ] and the related value extracted from ARPES is marked as rhombus, [ 56 ] γ ‐Al 2 O 3 /KTaO 3 , [ 44 ] EuO/KTaO 3 , [ 49 ] aLaAlO 3 /KTaO 3 [ 20 ] ), STO‐based systems (LaAl 1− x Mn x O 3 /SrTiO 3 (0 ≤ x ≤ 1), [ 31 ] γ ‐Al 2 O 3 /SrTiO 3 , [ 34 ] LaAlO 3 /SrTiO 3 , [ 8 ] LaAl 1− x Cr x O 3 /SrTiO 3 ( x = 0,0.1,0.2), [ 50 ] NiFe/LAO//STO [ 10 ] ) and semiconductors (InAlAs/InGaAs/InAlAs, [ 35 ] GaSe, [ 41 ] InP/InGaAs/InAlAs, [ 51 ] InGaAs/InAlAs, [ 52 ] GaN/AlGaN, [ 53 ] InSb, [ 37 ] InAs [ 54 ] ).…”

Oxide Spintronics as a Knot of Physics and Chemistry: Recent Progress and Opportunities

“…Moreover, they explored charge-to-spin conversion (direct Edelstein effect) in oxide 2DEGs for the first time by magneto-transport and quantified the Rashba coefficient of the system from bilinear magnetoresistance (BMR) and quadratic magnetoresistance (QMR) (Figure 3g). As a 5d wide-bandgap semiconductor, KTaO 3 can bridge the investigations of spin−charge conversion in 4d/5d heavy-metal oxides and interfacial 2D electron gases, 41,44 as shown in Figure 1.…”