Nonlocal Spin Diffusion Driven by Giant Spin Hall Effect at Oxide Heterointerfaces

Abstract

A two-dimensional electron gas emerged at a LaAlO/SrTiO interface is an ideal system for "spin-orbitronics" as the structure itself strongly couple the spin and orbital degree of freedom through the Rashba spin-orbit interaction. One of core experiments toward this direction is the nonlocal spin transport measurement, which has remained elusive due to the low spin injection efficiency to this system. Here we bypass the problem by generating a spin current not through the spin injection from outside but instead through the inherent spin Hall effect and demonstrate the nonlocal spin transport. The analysis on the nonlocal spin voltage, confirmed by the signature of a Larmor spin precession and its length dependence, displays that both D'yakonov-Perel' and Elliott-Yafet mechanisms involve in the spin relaxation at low temperature. Our results show that the oxide heterointerface is highly efficient in spin-charge conversion with exceptionally strong spin Hall coefficient γ ∼ 0.15 ± 0.05 and could be an outstanding platform for the study of coupled charge and spin transport phenomena and their electronic applications.

Study of equilibrium carrier transfer in LaAlO3/SrTiO3 from an epitaxial La1−x Sr x MnO3 ferromagnetic layer

“…In literature only a couple of cases report electric spin transfer from on-top magnetic electrodes into LAO/STO [18,19]. In particular, reference [18] reports transfer from FM Co electrodes with surprisingly long in-plane spin diffusion length of d spin ∼1 μm in the 2DEG, as estimated by Hanle effect, which is much larger than the estimate derived from the analysis of weak localization magnetoresistance [4], but consistent with estimates extracted from spin Hall effect in a non-local geometry [5]. In the same reference [18], the authors suggest that interface defects may play a role in amplifying the spin accumulation signal through a resonant tunneling mechanism.…”

“…It is demonstrated that both charge and spin of the conduction electrons in LAO/STO offer the possibility to manipulate and store digital information. Indeed, a strong Rashba spin-orbit coupling tunable by an applied gate voltage is observed [4,5], suggesting that transport of spin polarized carriers can be controlled by external parameters. Nevertheless, while charge transport in LAO/STO has been widely explored, spin transport remained an uncharted topic until very recently, at least on the experimental ground.…”

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO3–LaAlO3 Oxide Interface

“…Therefore, the STO/LAO heterostructure can enable potential spintronic innovations and now is attracting rising research interests. [8][9][10][11][12][13] Experimentally, Narayanapillai et al 8 have reported an extremely strong charge current induced Rashba field in the 2DEG layer, which verifies the presence of strong Rashba SOC predicted at the STO/LAO interface. Most recently, the inverse Edelstein effect at the STO/LAO interface has been demonstrated by using the spin pumping technique, [10][11][12] which shows a notable spin-to-charge conversion.…”

“…Additionally, a long spin diffusion length over 300 nm in the 2DEG channel has also been reported. 9,13 These observations suggest that the STO/LAO heterostructure can be a good spin detector as well as spin channel, which is promising to advance the realization of long sought spin transistors. However, the direct charge-to-spin conversion at the STO/LAO interface has not been demonstrated yet.…”

A possible superconductor-like state at elevated temperatures near metal electrodes in an LaAlO3/SrTiO3 interface

“…The interface formed between a LaAlO 3 (LAO) film and TiO 2 -terminated SrTiO 3 (STO) has a wide range of electronic phases, including superconductivity 1 , ferromagnetism 2 , and spin-orbit interactions 3–5 . These exotic phenomena open new opportunities to study fundamental issues in condensed matter physics, and the LAO/STO interface may be useful for future applications, such as field effect transistors 6–9 .…”