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

TL;DR

This paper investigates how the conductance of Dirac fermions on a topological insulator surface can be tuned by magnetic and potential barriers, revealing unique phenomena not seen in graphene, with potential applications in magnetic switching.

Contribution

It demonstrates the tunability of conductance behavior in topological insulator surface states via ferromagnetic exchange fields and potential barriers, highlighting phenomena absent in graphene.

Findings

Conductance transitions from oscillatory to monotonic with increasing exchange field.

Critical values of parameters change conductance maxima criteria.

Proposes experimental setups to observe these effects.

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 $\chi= e V_0 d/\hbar v_F = n \pi$ 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.