Unrestricted electron bunching at the helical edge
arXiv:1903.03965 · doi:10.1103/PhysRevLett.123.056803
The paper analytically studies how a magnetic impurity with spin S on the helical edge of a 2D time‑reversal‑invariant topological insulator causes backscattering and produces shot noise, showing that for S > 1/2 the Fano factor can become arbitrarily large, indicating strong electron bunching, while for S = 1/2 it remains bounded between 1 and 2.
Abstract
A quantum magnetic impurity of spin $S$ at the edge of a two-dimensional time reversal invariant topological insulator may give rise to backscattering. We study here the shot noise associated with the backscattering current for arbitrary $S$. Our full analytical solution reveals that for $S>\frac{1}{2}$ the Fano factor may be arbitrarily large, reflecting bunching of large batches of electrons. By contrast, we rigorously prove that for $S=\frac{1}{2}$ the Fano factor is bounded between $1$ and $2$, generalizing earlier studies.
6 pages, 2 figures, Supplemental Material