Mid-Term Report Summary - SPINBOUND (Exploring the Spin Physics at the Boundaries of Materials with Strong Spin-Orbit Interaction)
This project addresses a new research frontier on spin physics at the boundaries of materials with strong spin-orbit interaction (SOI). Although the properties of these materials have been studied for more than half a century, researchers are just starting to grasp the richness of SOI phenomena taking place at them. SOI leads to surface states with unusually large spin splitting in simple heavy elements such as gold or bismuth. It can also produce a nontrivial topology in band insulators, such as known thermoelectric material bismuth selenide, that brings about metallic boundary states with exotic spin textures that are protected by time reversal symmetry. Despite their fundamental and technological interest, information on the nature of charge transport at such surface states is scarce, while spin transport just starts to be explored. My team has studied the transport properties of topological insulator (TI) Bi2Se3. The devices were fabricated by mechanical exfoliation from bulk crystals. Notably it was found that, at low temperatures (< 50 K) and when the chemical potential lies inside the bulk gap, the crystal resistivity is strongly temperature dependent, reflecting inelastic scattering due to the thermal activation of optical phonons. A linear increase of the current with voltage is obtained up to a threshold value at which current saturation takes place. We demonstrated that the activated behaviour, the voltage threshold, and the saturation current can all be quantitatively explained by considering a single optical-phonon mode with energy ≈ 8 meV. This phonon mode strongly interacts with the surface states of the material and represents the dominant source of scattering at the surface at high electric fields. In addition, we have also initiated work on graphene based devices, on which graphene is modified with heavy adatoms such as gold. Theoretical work has demonstrated that the spin relaxation can be described by means of an entanglement between spin and pseudospin driven by random SOI, which is unique to graphene, resulting in fast spin dephasing with increasing relaxation times away from the charge neutrality point. Simultaneously, we have started fabricating spin devices based on graphene with large spin injection efficiencies and with suspended graphene in order to test the theoretical predictions. We demonstrated spin injection using amorphous carbon, which can now be included to the list of useful spin injector insulators, and have developed a process to suspend graphene using a single electron-beam resist, thus reducing contamination from processing. With these devices we have also developed a new means of investigating hot carrier propagation across graphene using an electrical nonlocal injection/detection method. We directly determine the carrier temperature and the characteristic cooling length for hot-carrier propagation, which are key parameters for a variety of new applications that rely on hot-carrier transport but that will also be present in spin transport devices.
Emma Gomez Maza
Tel.: +34 93 737 2634
Tel.: +34 93 737 2634
SubjectsElectronics and Microelectronics - Nanotechnology and Nanosciences - Physical sciences and engineering
Record Number: 183589 / Last updated on: 2016-06-16
Information source: SESAM