title: Tuning the conductance of dirac fermions on the surface of a topological insulator.
abstract: We study the transport properties of the Dirac fermions with a Fermi velocity v{F} on the surface of a topological insulator across a ferromagnetic strip providing an exchange field J over a region of width d. We show that the conductance of such a junction, in the clean limit and at low temperature, changes from oscillatory to a monotonically decreasing function of d beyond a critical J. This leads to the possible realization of a magnetic switch using these junctions. We also study the conductance of these Dirac fermions across a potential barrier of width d and potential V0 in the presence of such a ferromagnetic strip and show that beyond a critical J, the criteria of conductance maxima changes from chi=eV{0}d/variant Planck's over v{F}=npi to chi=(n+1/2)pi for integer n. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them.
authors.affiliation: Theoretical Physics Division, Indian Association for the Cultivation of Sciences, Kolkata 700 032, India.
authors.forename: S
authors.initials: S
authors.lastname: Mondal
authors.forename: D
authors.initials: D
authors.lastname: Sen
authors.forename: K
authors.initials: K
authors.lastname: Sengupta
authors.forename: R
authors.initials: R
authors.lastname: Shankar