Spin Coherence and Magnetism in Graphene

University Of California-Riverside, Riverside CA

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** Electrons possess a fundamental property known as spin, which makes the electron equivalent to a small magnet. The long term goal of this project is to develop a powerful new type of computer known as a "spin computer" that uses the electron spin to store and process data. The design of this type of computer has been developed for electron spins in semiconductors, but such efforts have been hampered by small signals and the need for cryogenic (very low) operating temperatures. The advent of a new electronic material known as graphene, a single atomic sheet of carbon, is making the prospects of a spin computer more realistic because large spin signals have been demonstrated at room temperature. This project will advance the fundamental knowledge of electron spin in graphene by performing experiments that investigate the role of imperfections such as impurities, vacancies, and ripples in the graphene sheet. These studies are crucial because imperfections are believed to be responsible for the loss of information held by the electron spin ("decoherence"), although it is currently unclear which type of imperfection is the main source of the problem. The experiments will systematically address this critical issue and also explore new methods of using the imperfections to control the alignment of the spins ("magnetism"). This project will support the training of a PhD student, an undergraduate student, and a high school student in condensed matter physics using state-of-the-art instrumentation. The knowledge gained in these studies will greatly broaden the scientific and technological impact of spintronics. ****TECHNICAL ABSTRACT**** The origin of spin scattering in graphene is a central issue of graphene spintronics, while tunable magnetism is a fascinating collective phenomena predicted for doped and/or defective graphene. This project investigates spin scattering and tunable magnetism by systematically introducing impurities, vacancies, and ripples into graphene spin valves and Hall bar devices. The experimental approach combines the techniques of molecular beam epitaxy (MBE) and magnetotransport measurements in a unique manner. Impurities will be systematically introduced atom-by-atom through MBE deposition while vacancies will be generated by Ar-ion sputtering in an ultrahigh vacuum chamber. Their effect on charge and spin transport will be measured in the same chamber via in situ magnetotransport measurements. Ripples will be controlled through the use of atomically flat substrates produced by MBE. The effects of these types of disorder on spin lifetimes will be measured by spin precession (Hanle) measurements on spin valves and will elucidate the mechanism of spin scattering in graphene. The Kondo effect and gate tunable magnetic ordering in doped and/or defective graphene will be investigated through a combination of magnetotransport measurements and magnetization measurements. These experiments will greatly expand the knowledge of spin-dependent interactions in solid-state systems and provide excellent training for a PhD student, an undergraduate student, and a high school student in condensed matter physics.