Finite frequency backscattering current noise at a helical edge

TL;DR

This paper analyzes the finite-frequency backscattering current noise at a helical edge coupled to magnetic impurities, revealing Fano-type resonances and non-monotonic bias dependence, which deepen understanding of edge conductance deviations.

Contribution

It provides a theoretical calculation of backscattering current noise at finite frequencies for a helical edge with arbitrary spin impurities, including resonance features and their dependence on system parameters.

Findings

Presence of Fano-type resonances at non-zero frequencies.

Resonance widths are determined by Korringa rates.

Backscattering noise exhibits non-monotonic bias dependence.

Abstract

Magnetic impurities with sufficient anisotropy could account for the observed strong deviation of the edge conductance of 2D topological insulators from the anticipated quantized value. In this work we consider such a helical edge coupled to dilute impurities with an arbitrary spin $S$ and a general form of the exchange matrix. We calculate the backscattering current noise at finite frequencies as a function of the temperature and applied voltage bias. We find that in addition to the Lorentzian resonance at zero frequency, the backscattering current noise features Fano-type resonances at non-zero frequencies. The widths of the resonances are controlled by the spectrum of corresponding Korringa rates. At a fixed frequency the backscattering current noise has non-monotonic behaviour as a function of the bias voltage.