Room Temperature Charge-Spin Interconversion in a Topological Insulator and Graphene Heterostructure

Abstract

The main goal of spintronics is to utilise the spin degree of freedom beyond conventional charge-based technologies and make faster and less energy-consuming nonvolatile information technology. To realise this, efficient generation, transport and detection of polarised spin are necessary. Topological insulators are emerging materials for spin generation and detection in all-electrical spintronics applications, thanks to their strong spin-orbit coupling and the non-trivial spin-momentum locking of their unique topological surface states. Due to the efficient charge-to-spin conversion process, applying a bias current to induce a net carrier momentum should spontaneously generate a net spin polarisation in such a system. However, while charge-spin interconversion in topological insulators has previously been reported, reliable non-local measurements have so far been limited to cryogenic temperatures. In this master’s thesis, charge-to-spin and spin-to-charge conversion in the topological insulator Bi1.5Sb0.5Te1.7Se1.3 are detected in a non-local measurement method at room temperature, using a van der Waals heterostructure with a graphene spin valve device. These heterostructures make it possible to combine the spin polarisation of the topological insulator with the excellent spin transport properties of graphene. The observation of both spin switch and Hanle spin precession signals in the non-local geometry and detailed bias- and gate-dependent measurements prove the robustness of the charge-spin interconversion effects in topological insulators at room temperature. These findings demonstrate the possibility of using topological insulators to make all-electrical room-temperature spintronics devices.