• Aug 03 2011

    Izak Snyman

    NITheP cordially invites you to a seminar by:

    Dr Izak Snyman
    National Institute for Theoretical Physics, Stellenbosch

    Date: Wednesday 3rd of August 2011
    Time: 14:00
    Venue: NITheP Stellenbosch Seminar room

    TITLE: The quantum Hall effect in carbon nanotubes

    ABSTRACT: The quantum Hall effect (a Hall conductivity quantized in integer units of e^2/h) is regularly observed in a two dimensional electron gas in a constant magnetic field perpendicular to the plane of the electrons. The effect can be explained by noting that the electron gas becomes incompressible when the number of electrons is an integer multiple of the total magnetic flux through the sample in units of h/e.
    However, a more general theory for the Hall effect exits, [Q. Niu, D. J. Thouless, and Y.-S. Wu, Phys. Rev. B 31, 3372, (1985)] in which the Hall conductance is related to a two dimensional topological invariant. I will illustrate just how general this theory is, by considering a carbon nanotube. I will show that a gap is induced around the Fermi energy in the electronic spectrum of a previously metallic nanotube, in the presence of electric and magnetic fields perpendicular to the tube axis.
    For realistic values of the fields, a gap of at least a few meV can appear. Despite the quasi-one dimensional nature of the system, the gapped state is associated with a non-zero topological invariant and supports a Hall effect. This is revealed when the flux through the tube is varied by one flux quantum, which leads to exactly one electron per spin being transported between the ends of the tube. It is interesting that the Hall effect is present even though the total magnetic flux through the tube wall is zero.

    Navrae/Enquiries: Prof M Kastner
    Tel: 021 808 3863
    Email: kastner@sun.ac.za