Current noise from a magnetic moment in a helical edge

Abstract

We calculate the two-terminal current noise generated by a magnetic moment coupled to a helical edge of a two-dimensional topological insulator. When the system is symmetric with respect to in-plane spin rotation, the noise is dominated by the Nyquist component even in the presence of a voltage bias $V$. The corresponding noise spectrum $S(V,\omega )$ is determined by a modified fluctuation-dissipation theorem with the differential conductance $G(V,\omega )$ in place of the linear one. The differential noise $\partial S/\partial V$, commonly measured in experiments, is strongly dependent on frequency on a small scale ${\tau }_K^{-1}\ll T$ set by the Korringa relaxation rate of the local moment. This is in stark contrast with the case of conventional mesoscopic conductors where $\partial S/\partial V$ is frequency-independent and defined by the shot noise. In a helical edge, a violation of the spin-rotation symmetry leads to the shot noise, which becomes important only at a high bias. Uncharacteristically for a fermion system, this noise in the backscattered current is super-Poissonian.

Improved presentation and added references, now 6+3 pages, 2 figures

References in corpus (14)

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Cited by in corpus (5)

• Quantum Fluctuation of the Quantum Geometric Tensor and its Manifestation as Intrinsic Hall Signatures in Time-Reversal Invariant Systems
• Finite frequency backscattering current noise at a helical edge
• Unidirectional magneto-transport of linearly dispersing topological edge states
• Electrically-detected single-spin resonance with Quantum Spin Hall edge states
• Finite-frequency admittance and noise of a helical edge coupled to a magnet