Tuning the conductance of Dirac fermions on the surface of a topological insulator

Abstract

We study the transport properties of the Dirac fermions with Fermi velocity $v_F$ on the surface of a topological insulator across a ferromagnetic strip providing an exchange field $\mathcal{J}$ over a region of width $d$. We show that the conductance of such a junction changes from oscillatory to a monotonically decreasing function of $d$ beyond a critical $\mathcal{J}$. 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 $V_0$ in the presence of such a ferromagnetic strip and show that beyond a critical $\mathcal{J}$, the criteria of conductance maxima changes from $\ddot{I}‡=e{V}_{0}d/\hslash v_F=n\ddot{I}€$ to $\ddot{I}‡=(n+1/2)\ddot{I}€$ for integer $n$. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them.

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