The spin-orbit interaction couples the electrons' motion to their spin. Accordingly, passing a current in a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice-versa (inverse spin Hall effect, ISHE) 1-3 . The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronics functionalities 4,5 and devices, some of which do not require any ferromagnetic material 6 . However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronics hetero-and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism the Rashba effect 7 in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin-pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES. Perovskite oxide materials possess a broad range of functionalities, some of which can be very appealing for spintronics. This includes half-metallicity in mixed-valence manganites that can be used to produce giant tunnel magnetoresistance 8 or multiferroicity through which magnetization direction can be electrically controlled at low power 9 . The recent years have seen the emergence of novel spintronics effects based on the generation and control of pure spin currents through spin-orbit effects in semiconducting and metallic systems 1-3 . However, despite a renewal of interest for 4d and 5d transition metal perovksites 10 , spin-orbit effects remained largely unexplored in oxide spintronics.An emerging direction in oxide research aims at discovering novel electronic phases at interfaces between two oxide materials 11 . A well-known example is the LaAlO3/SrTiO3 system: while both LaAlO3 (LAO) and SrTiO3 (STO) are wide bandgap semiconductors, a high-mobility two-dimensional electron system (2DES) forms at their interface 12 if the LAO thickness is at least 4 unit-cells (uc). Interestingly, LAO/STO possesses several remarkable extra functionalities including a gate-tuneable Rashba effect 13,14 , which makes it particularly appealing for spintronics.The Rashba effect is a manifestation of the spin-orbit interaction (SOI) in solids, where spin degeneracy associated with the spatial inversion symmetry is lifted due to a symmetry-breaking electric field normal to an heterointerface 15 . In a Rashba 2DES, the flow of a charge current results in the creation of a nonzero spin accumulation 16,17 coming from uncompensated spin-textured Fermi surfaces. Recently, the converse effect so-called inverse Edelstein effect (IEE) that is a spin-to-charge conversion through SOI was discovered a...
1We present experimental results on the conversion of a spin current into a charge current by spin pumping into the Dirac cone with helical spin polarization of the elemental topological insulator (TI) α- The Inverse Edelstein Effect 5,6,17 (IEE) can be described as the inverse conversion of the one in EE. As depicted in Fig.1e-f, the injection of a vertical spin current into the 2DEG at a Rashba or TI surface/interface induces a charge current in the 2DEG. The IEE length 5 IEE is the ratio between the 2D conventional charge current density (in A/m) induced by IEE in the surface/interface 2DEG and the injected 3D spin current density, . We adopt the usual definition with the injected spin current density with equal to the difference between the injected charge current densities carried by electrons having their spin respectively oriented along the +i and -i directions along the x-or y-axis (the corresponding injected spin flow density is /(2e) where e= -|e|). For both Rashba and TI interfaces, and in the simple situation of circular spin contours, IEE can be expressed as a function of the relaxation time τ of an out of equilibrium distribution in the topological states by the following, where α R is the Rashba coefficient, and, as derived infor TI, where v F is the Fermi velocity of the DC. To be more precise on the sign, our definition of the IEE length is exactlywhere the upper ( In the ARPES images of Fig. 2, a DC is clearly seen at the free surface (top) of our α-Sn (001) Supplementary Fig. 2). We can thus expect that only the α-Sn/Ag/Fe samples will show SCC by IEE. This is confirmed by the results displayed in Fig. 3b-c: i) A large enhancement of the damping coefficient revealing significant spin absorption is seen in Fig. 3b only for α-Sn/Ag/Fe and not for α-Sn/Fe. ii) In Fig. 3c, a dc charge current I C peak at the resonance is only seen for α- An important parameter in equation (1) ARPES measurements. The ARPES measurements were performed at room temperature with incident photon energy of 19 eV and resolving angle between 15° which correspond to wave number k between 5 nm -1 at the Fermi level. In Fig. 2, only the area of interest is shown.Ferromagnetic resonance (FMR) and spin pumping. The samples have the stacking order shown in Fig. 3.The broadband frequency dependence was performed in a coplanar wave guide system, applying the external magnetic film at different in-plane crystalline directions of the substrate. The samples were then cut in slab of 2.4x0.4 mm to carry out the simultaneously FMR and transversal dc voltage measurement (Fig. 3a,c). The slab is placed on the axis of a cylindrical X-band cavity (frequency ≈ 9.6 GHz). The charge current I C is derived from the voltage V needed to cancel it, I c = V/R where R is the resistance of the sample measured between the voltage probes.5
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