Condensed Matter Seminar

Dr. Chris Ford
University of Cambridge, UK

Thursday, October 8, 2009
1:00 pm in SPL 52

Investigation of the spin states of a quantum antidot by selective injection and detection

Abstract: In light of recent experiments demonstrating the potential of nanostructures in the integer quantum Hall (IQH) regime for the coherent manipulation of electrons through edge states, we have begun to explore the potential for spin control in such systems, in order to utilise both long spin-coherence timescales and controllable electron transport along edge states. Here we describe new measurements of spin-resolved transport through a quantum antidot (AD) in the IQH regime with potentially exciting applications for spin manipulation. Our device employs quantum point contacts to selectively inject and detect non-equilibrium edge-state populations through an AD, allowing us to probe the spin structure of AD states. Surprisingly, we find that most resonances at AD filling factor nu = 2 show contributions from both spin channels, rather than spin-polarised transport of alternating polarity as standard theories predict. Moreover, while in most cases the initial spin of the transported electron is conserved, we have discovered specific regimes in which a fraction of the injected current shows a spin flip during transmission through the AD. No existing model of AD states successfully accounts for all the observations, which seem to imply that spin excitations have much lower energies than charge excitations, as for a maximum-density droplet.