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

In this letter, we report on electrical spin injection and detection in n-type germanium-on-insulator using a Co/Py/Al2O3 spin injector and 3-terminal non-local measurements. We observe an enhanced spin accumulation signal of the order of 1 meV consistent with the sequential tunneling process via interface states in the vicinity of the Al2O3/Ge interface. This spin signal is further observable up to 220 K. Moreover, the presence of a strong inverted Hanle effect points out the influence of random fields arising from interface roughness on the injected spins.