Shot noise in helical edge states in presence of a static magnetic defect

The Fano factor, $\mathcal{F},$ of the shot noise of the current through the edge states of a two-dimensional topological insulator with contacts of generic type is calculated. A magnetic static defect changes $\mathcal{F}$ significantly. For metallic contacts, as the strength of the defect increases, the Fano factor increases from $\mathcal{F} = 0$ to its maximum value, ${{\mathcal{F}}_{{{\text{max}}}}} \approx 0.17,$ and then decreases back to zero value in the limit of strong defect. For tunnel contacts in the limit of weak tunnel coupling, the Fano factor is insensitive to the strength of the defect: $\mathcal{F} \to 1{\text{/}}2.$ For weak but finite tunnel coupling strength, $\mathcal{F}$ exhibits a periodic series of sharp peaks of small amplitude as a function of the magnetic flux piercing the sample. The peaks transform into Aharonov–Bohm harmonic oscillations with increasing the strength of the tunnel coupling.