Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
Nat Commun. 2014 Jun 6;5:4067. doi: 10.1038/ncomms5067.
The fractional quantum Hall effect is a canonical example of topological phases. While electric currents flow downstream in edge modes, neutral edge modes, observed only in hole-conjugate states and in ν=5/2, flow upstream. It is believed that the latter transport results from multiple counter-propagating channels-mixed by disorder that is accompanied by Coulomb interaction. Here we report on sensitive shot noise measurements that reveal unexpected presence of neutral modes in non-hole-conjugate fractional states; however, not in the integer states. Furthermore, the incompressible bulk is also found to allow energy transport. While density reconstructions along the edge may account for the energy carrying edge modes, the origin of the bulk energy modes is unidentified. The proliferation of neutral modes changes drastically the accepted transport picture of the fractional quantum Hall effects. Their apparent ubiquitous presence may explain the lack of interference of fractional quasiparticles-preventing observation of fractional statistics.
分数量子霍尔效应是拓扑相的典型范例。在边缘模式中，电流向下游流动，而在中性边缘模式中，仅在空穴共轭态和 ν=5/2 中观察到向上游流动。据信，后者的传输是由多个反向传播的通道引起的，这些通道由于伴随库仑相互作用的无序而混合在一起。在这里，我们报告了灵敏的散粒噪声测量结果，这些结果显示出出乎意料的中性模式存在于非空穴共轭分数量子态中；然而，在整数态中则不存在。此外，还发现不可压缩的体相也允许能量传输。虽然沿边缘的密度重构可以解释携带能量的边缘模式，但体相能量模式的起源尚不清楚。中性模式的大量出现极大地改变了分数量子霍尔效应的公认传输图景。它们明显的普遍存在可能解释了分数量子粒子缺乏干涉的原因，从而阻止了分数量子统计的观测。
