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 X=eV₀d/ћv_F=nπ to X=(n+½)π for integer n. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them.