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Finite-frequency admittance and noise of a helical edge coupled to a magnet

Oliver Franke1, Paula Koll1, Peter G. Silvestrov2, and Piet W. Brouwer1

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Phys. Rev. B 113, 045105 – Published 2 January, 2026

DOI: https://doi.org/10.1103/yj56-jtxd

Abstract

The exchange coupling of the helical edge state of a quantum spin-Hall insulator with an easy-plane magnet has no effect on its dc electrical conductance if the magnet's anisotropy axis is aligned with the spin-quantization axis of the helical edge state [Meng et al., Phys. Rev. B 90, 205403 (2014)]. We here calculate the ac conductance GV(ω) and the noise power SV(ω) in the presence of a dc bias V. While both take the universal values GV(ω=0)=e2/h and SV(ω=0)=4e2kBT/h in the zero-frequency limit, GV(ω) and SV(ω) are quickly suppressed for finite ω, so that low-frequency transport is effectively noiseless.

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Phys. Rev. B 113, 045105– Published 2 January, 2026
  • Received 4 November 2025
  • Accepted 11 December 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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