Giant spin-to-charge conversion at an all-epitaxial single-crystal-oxide Rashba interface with a strongly correlated metal interlayer

Abstract

The two-dimensional electron gas (2DEG) formed at interfaces between SrTiO3 (STO) and other oxide insulating layers is promising for use in efficient spin-charge conversion due to the large Rashba spin-orbit interaction (RSOI). However, these insulating layers on STO prevent the propagation of a spin current injected from an adjacent ferromagnetic layer. Moreover, the mechanism of the spin-current flow in these insulating layers is still unexplored. Here, using a strongly correlated polar-metal LaTiO3+δ (LTO) interlayer and the 2DEG formed at the LTO/STO interface in an all-epitaxial heterostructure, we demonstrate giant spin-to-charge current conversion efficiencies, up to ~190 nm, using spin-pumping ferromagnetic-resonance voltage measurements. This value is the highest among those reported for all materials, including spin Hall systems. Our results suggest that the strong on-site Coulomb repulsion in LTO and the giant RSOI of LTO/STO may be the key to efficient spin-charge conversion with suppressed spin-flip scattering. Our findings highlight the hidden inherent possibilities of oxide interfaces for spin-orbitronics applications.

Spin-charge interconversion of two-dimensional electron gases at oxide interfaces

“…Therefore, as temperature (T) decreases, λ IEE increases significantly. Notably, Kaneta-Takada et al [24] achieved a giant λ IEE of 193.5 nm at 15 K, which is the highest value reported among all materials including spin Hall systems.…”

“…In order to achieve a larger IEE efficiency, a larger α R , a larger momentum/spin relaxation time (τ) and efficient spin current propagation are required. Recently, Kaneta-Takada et al [24] used strongly correlated polar metal LaTiO 3+δ (LTO) layers to carefully cultivate high-quality fully epitaxial LSMO/LTO/ STO heterostructures via molecular beam epitaxy (MBE), which is shown in figure 7(c). They demonstrated a large spin-tocharge conversion efficiency using spin pumping ferromagnetic resonance voltage measurements.…”

“…This spurred intensive research on the origins of 2DEGs, and soon after various STO-based heterointerfaces were fabricated to produce 2DEGs [2][3][4][5][6][7]. Diverse phenomena have been observed at the interface, including ultrahigh mobility [8], interfacial magnetism [9] superconductivity [10][11][12], gate tunable Rashba effect [13][14][15][16] and spin-charge interconversion [17][18][19][20][21][22][23][24][25][26][27][28]. Among them, the latter two effects are particularly attractive in the sense that they provide opportunities to incorporate spin-orbitronic functionalities into 2DEGs.…”