Väyrynen JI, Glazman LI. Current Noise from a Magnetic Moment in a Helical Edge.
PHYSICAL REVIEW LETTERS 2017;
118:106802. [PMID:
28339237 DOI:
10.1103/physrevlett.118.106802]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Indexed: 06/06/2023]
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,ω) is determined by a modified fluctuation-dissipation theorem with the differential conductance G(V,ω) in place of the linear one. The differential noise ∂S/∂V, commonly measured in experiments, is strongly dependent on frequency on a small scale τ_{K}^{-1}≪T set by the Korringa relaxation rate of the local moment. This is in stark contrast to the case of conventional mesoscopic conductors where ∂S/∂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.
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