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.

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

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• Quantum Fluctuation of the Quantum Geometric Tensor and its Manifestation as Intrinsic Hall Signatures in Time-Reversal Invariant Systems
• Fluctuation dissipation relations for strongly correlated out-of-equilibrium circuits
• Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations
• Unrestricted electron bunching at the helical edge
• Finite frequency backscattering current noise at a helical edge
• Noise in the helical edge channel anisotropically coupled to a local spin
• Protection of Edge transport in Quantum Spin Hall samples: Spin-Symmetry Based General Approach and Examples
• Shot noise as a probe of spin-correlated transport through single atoms
• The effect of magnetic impurity scattering on transport in topological insulators
• Suppression of ballistic helical transport by isotropic dynamical magnetic impurities
• Electron-pairing in the quantum Hall regime due to neutralon exchange
• Sub- to Super-Poissonian crossover of current noise in helical edge states coupled to a spin impurity in a magnetic field
• Electrically-detected single-spin resonance with Quantum Spin Hall edge states
• Unidirectional magneto-transport of linearly dispersing topological edge states
• Finite-frequency admittance and noise of a helical edge coupled to a magnet