Magnetic moments in a helical edge can make weak correlations seem strong

TL;DR

This paper investigates how magnetic impurities affect the conductance of helical edges, revealing that backscattering from local moments causes a power-law suppression of conductance, which can mimic strong electron-electron interactions.

Contribution

It provides a new interpretation of conductance suppression in helical edges due to magnetic moments, contrasting with previous explanations based on electron repulsion.

Findings

Backscattering off magnetic moments leads to power-law conductance suppression.

The conductance behavior mimics effects of strong electron-electron interactions.

Results explain recent experimental observations without requiring fine-tuned electron repulsion.

Abstract

We study the effect of localized magnetic moments on the conductance of a helical edge. Interaction with a local moment is an effective backscattering mechanism for the edge electrons. We evaluate the resulting differential conductance as a function of temperature $T$ and applied bias $V$ for any value of $V/T$. Backscattering off magnetic moments, combined with the weak repulsion between the edge electrons results in a power-law temperature and voltage dependence of the conductance; the corresponding small positive exponent is indicative of insulating behavior. Local moments may naturally appear due to charge disorder in a narrow-gap semiconductor. Our results provide an alternative interpretation of the recent experiment by Li et al. \cite{Li15} where a power-law suppression of the conductance was attributed to strong electron repulsion within the edge, with the value of Luttinger liquid parameter $K$ fine-tuned close to $1/4$.