Väyrynen Jukka I, Glazman Leonid I
Department of Physics, Yale University, New Haven, Connecticut 06520, USA.
Phys Rev Lett. 2017 Mar 10;118(10):106802. doi: 10.1103/PhysRevLett.118.106802.
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.
我们计算了与二维拓扑绝缘体的螺旋边缘耦合的磁矩所产生的双端电流噪声。当系统关于面内自旋旋转对称时，即使存在电压偏置V，噪声也主要由奈奎斯特分量主导。相应的噪声谱S(V,ω)由修正的涨落耗散定理确定，其中用微分电导G(V,ω)代替了线性电导。实验中通常测量的微分噪声∂S/∂V在由局域磁矩的科林加弛豫率设定的小尺度τ_{K}^{-1}≪T上强烈依赖于频率。这与传统介观导体的情况形成鲜明对比，在传统介观导体中∂S/∂V与频率无关且由散粒噪声定义。在螺旋边缘，自旋旋转对称性的破坏会导致散粒噪声，这种噪声仅在高偏置时才变得重要。对于费米子系统而言不寻常的是，反向散射电流中的这种噪声是超泊松分布的。
