"Topological insulators and Rashba interfaces as efficient converters of spin to charge current: towards low power consumption and energy harvesting "

Who: Carlos Rojas-Sánchez, Institut Jean Lamour -CNRS/Univ. Lorraine, Nancy, France

Place: nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian

Date: Monday, 7 May 2018, 11:00

Materials with large efficiency of spin-charge current interconversion are highly desirable to study new physical phenomena as well as for spintronics applications. Heavy metals or alloys exhibiting large spin-orbit coupling such as Pt, Ta or W scatter the electrons in opposite directions when they have opposite spin. Thus an injection of charge current yields a spin current in such materials. That charge-spin current conversion phenomenon in those 3D materials is so-called Spin Hall Effect (SHE). We can exploit this effect to manipulate a magnetization in a heavy metal/ferromagnetic structure (HM/FM) as in current-induced magnetization switching experiments or current-switching of magnetization [1-3]. We have just shown current-induced magnetization switching in Si-SiO2//W(3 nm)/CoxTb1-x(3.5 nm)/Al(3 nm) structures. Interesting, we have found out that the temperature of the devices reach a characteristic temperature just before the switching takes place. This temperature is not the magnetic compensation temperature neither the angular compensation temperature of the CoTb ferrimagnetic alloy [3]. 

On the other hand, new classes of materials such as 3D topological insulator which are trivial insulator in their bulk but hold metallic states in their surfaces are also highly interesting for spintronics. The spin-orbit coupling (SOC) in the 2DEG states at Topological Insulator (TI) or Rashba Interfaces is predicted to be more efficiency that their 3D counterparts for spin-charge current conversion. Indeed, we have found the highest efficiency at room temperature using the topological insulator ?-Sn [4]. The underlying physics of charge-spin current interconversion in such 2D systems is different of the SHE and is called Edelstein Effect (EE) [5-7], also known as inverse spin galvanic effect [8]. I will show results of spin-to-charge conversion by spin pumping experiments and their analysis in term of inverse Edelstein Length [4-7]. Experimental results based on ARPES and spin pumping indicate that direct contact of metallic ferromagnetic layer is detrimental for the surfaces states of topological insulators but we can keep the surfaces states of ?-Sn using Ag spacer. I will use the conversion parameters obtained at room temperature with ?-Sn to demonstrate the very large advantage of the SOC effects in 2D interface states with respect to the Spin Hall Effect (SHE) of 3D metals and the resulting perspective for low power spintronic devices. I will focus especially in the prediction of giant spin Seebeck effect using insulator ferrimagnet Y3Fe5O12 (YIG) in YIG/?-Sn films structures. 

[1] M. Miron, P. Gambardella et al. Nat. 476, 189 (2011) 
[2] J.-C. Rojas-Sánchez et al. Appl. Phys. Lett. 108, 082406 (2016) 
[3] T. H.Pham et al. arXiv 1711.10790 
[4] J.-C. Rojas-Sánchez et al. Phys. Rev. Lett. 116, 096602 (2016). ArXiv 1509.02973 (2015) 
[5] J.-C. Rojas-Sánchez et al. Nat. Comm 4, 2943 (2013) 
[6] E. Lesne, J.-C. Rojas-Sánchez et al. Nat. Mat. 15, 1261 (2016) 
[7] S. Oyarzun, J.-C. Rojas-Sánchez et al. Nat. Comm. 7, 13857 (2016) 
[8] S. D. Ganichev et al. Nature 417, 153 (2002)

Host: F. Casanova

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