Interference effects induced by a precessing easy-plane magnet coupled to a helical edge state

TL;DR

This paper investigates how a precessing easy-plane magnet coupled to a helical edge state in a topological insulator influences electronic transport, revealing AC current generation and conditions for observing the Aharonov-Bohm effect.

Contribution

It introduces a theoretical model of a magnet embedded in an interferometer with helical edges, showing how it induces AC currents and affects quantum interference effects.

Findings

Magnet presence causes AC currents under DC bias.

DC Aharonov-Bohm effect is suppressed at low temperature and voltage.

Effect depends on magnet-induced excitation gap.

Abstract

The interaction of a magnetic insulator with the helical electronic edge of a two-dimensional topological insulator has been shown to lead to many interesting phenomena. One of these is that for a suitable orientation of the magnetic anisotropy axis, the exchange coupling to an easy-plane magnet has no effect on DC electrical transport through a helical edge, despite the fact that it opens a gap in the spectrum of the helical edge [Meng {\em et al.}, Phys.\ Rev.\ B {\bf 90}, 205403 (2014)]. Here, we theoretically consider such a magnet embedded in an interferometer, consisting of a pair of helical edge states connected by two tunneling contacts, at which electrons can tunnel between the two edges. Using a scattering matrix approach, we show that the presence of the magnet in one of the interferometer arms gives rise to AC currents in response to an applied DC voltage. On the other hand, the DC Aharonov-Bohm effect is absent at zero temperature and small DC voltages, and only appears if the applied voltage or the temperature exceeds the magnet-induced excitation gap.