Tunneling Aharonov-Bohm interferometer on helical edge states

TL;DR

This paper investigates the transport properties of a helical edge state interferometer under magnetic flux, revealing flux-dependent antiresonances caused by magnetic impurities and proposing potential for flux-tunable magnetic disorder control.

Contribution

It introduces a detailed analysis of flux-dependent conductance behavior in helical edge state interferometers with magnetic impurities, highlighting antiresonances and interference effects.

Findings

Conductance shows sharp antiresonances at half-integer flux quanta due to magnetic impurities.

Interference of multiple return paths enhances backscattering at specific flux values.

Quantum correction to conductance is proportional to a flux-dependent ballistic Cooperon.

Abstract

We discuss transport through interferometer formed by helical edge states tunnel-coupled to metallic leads. We focus on the experimentally relevant case of relatively high temperature as compared to the level spacing and discuss a response of the setup to the external magnetic flux $\phi$ (measured in units of flux quantum) piercing the area encompassed by edge states. We demonstrate that tunneling conductance of the interferometer is structureless in ballistic case but shows a sharp antiresonances, as a function of magnetic flux $\phi$ - with the period 1/2 - in the presence of magnetic impurity. We interpret the resonance behavior as a coherent enhancement of backward scattering off magnetic impurity at integer and half-integer values of flux, which is accompanied by suppression of the effective scattering at other values of flux. Both enhancement and suppression are due to the interference of processes with multiple returns to magnetic impurity after a number of clockwise and counterclockwise revolutions around setup. This phenomenon is similar to the well-known weak-localization-induced enhancement of backscattering in disordered systems. The quantum correction to the tunneling conductance is shown to be proportional to flux-dependent "ballistic Cooperon". The obtained results can be used for flux-tunable control of the magnetic disorder in Aharonov-Bohm interferometers built on helical edge states.