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

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.[Phys. Rev. Lett. 115, 136804 (2015)] 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.