Abstract EN:

This thesis is composed by four chapters. In the first, we start by introducing basic concepts in spintronics, such as the electron spin, a definition of spin current, and how spins behave in real materials. Then, we review the main consequences of the relation between charge and spin currents in different materials, and how a charge current can be converted in a spin current (and vice-versa). In particular scenarios, the physics of the interconversion follows special symmetry considerations in the framework of the Dressllehaus and Rashba effects, which in turn explain the spin-to-charge current interconversion in 2D electron gases through the direct and inverse Edelstein effect. In the second chapter, we introduce the main material used throughout this thesis: strontium titanate (SrTiO3). After reviewing its main features, we explore the remarkable 2D elec-tron gas found in the LaAlO3/SrTiO3 system. We discuss in detail the origin of the interfacial conductivity that arises between these two insulators, the critical thickness for conduction of 4 unit cells of LaAlO3, and the main mechanisms that lead to the 2D electron gas formation (polar catastrophe, cation interdiffusion, surface reactions and polarity-induced defects). Then, we thoroughly describe the experimental procedure to obtain such heterostructures, including a comprehensive guide on the surface treatment of SrTiO3 single crystals, the pulsed laser deposition growth of ultra-thin LaAlO3 films and magnetron sputtering. In addition, we elaborate on the two main techniques used to evaluate the interfacial properties, X-ray photoelectron spectroscopy and magnetotransport, while showing some results for LaAlO3/SrTiO3 samples. Lastly, we show how a thin deposition of a metallic layer on top of LaAlO3/SrTiO3 can drastically change the interfacial properties, by reducing (if the metal is reactive) or increasing (for noble metals) the critical thickness for conduction. We end this chapter by giving a blueprint that describes how a 2D electron gas can be created in other oxide systems. In the third chapter we investigate spin-tocharge conversion phenomena. We start by giving an overview on experimental observations of Rashba 2D electron gases, as well as spin-to-charge current conversion through the inverse Edelstein effect in semiconductor quantum wells, topological insulators and oxide-based systems. Then, we thoroughly introduce spin pumping, a technique used to generate pure spin currents. Results for spin-to-charge current conversion in the LaAlO3/SrTiO3 and metal-capped SrTiO3 systems are shown, accompanied by an interpretation of the large and tunable conversion efficiency. For the metal-capped SrTiO3 case, angle-resolved photoemission spectroscopy and notions of electronic band mixing and topology are introduced to describe the extremely large efficiency. In the last chapter, we show additional experiments performed on the LaAlO3/SrTiO3 system regarding anisotropic and unidirectional magnetoresistance, while reviewing the scarce bibliography on these effects in 2D electron gases. After that, we introduce a recently discovered effect, the unidirectional spin Hall magnetoresistance, and develop a simple conceptual model for an analogous effect in 2D electron gases: the unidirectional Edesltein magnetoresistance. This effect is based on the expected strong charge-to-spin conversion in 2D electrons gas, and the interaction of the generated spin currents with an adjacent ferromagnet. We finish by very briefly showing preliminary experiments in NiFe/ LaAlO3/SrTiO3 heterostructures.