Max Planck Institute for the Physics of Complex Systems, Dresden, Germany.
Phys Rev Lett. 2010 Apr 23;104(16):166803. doi: 10.1103/PhysRevLett.104.166803. Epub 2010 Apr 22.
The quantum spin Hall (QSH) state, observed in a zero magnetic field in HgTe quantum wells, respects the time-reversal symmetry and is distinct from quantum Hall (QH) states. We show that the QSH state persists in strong quantizing fields and is identified by counterpropagating (helical) edge channels with nonlinear dispersion inside the band gap. If the Fermi level is shifted into the Landau-quantized conduction or valence band, we find a transition between the QSH and QH regimes. Near the transition the longitudinal conductance of the helical channels is strongly suppressed due to the combined effect of the spectrum nonlinearity and enhanced backscattering. It shows a power-law decay B(-2N) with magnetic field B, determined by the number of backscatterers on the edge N. This suggests a rather simple and practical way to probe the quality of quasiballistic QSH devices using magnetoresistance measurements.
量子自旋霍尔(QSH)态在 HgTe 量子阱中零磁场下被观测到，它遵守时间反演对称，与量子霍尔(QH)态不同。我们表明，QSH 态在强量子化场中仍然存在，并通过带隙内具有非线性色散的反向传播(螺旋)边缘通道来识别。如果费米能级被转移到 Landau 量子化的导带或价带中，我们会发现 QSH 和 QH 区之间的转变。在转变附近，由于谱非线性和增强的反向散射的综合影响，螺旋通道的纵向电导被强烈抑制。它显示出与磁场 B 的幂律衰减 B(-2N)，由边缘上的反向散射器的数量 N 决定。这表明了一种使用磁阻测量来探测准弹道 QSH 器件质量的简单而实用的方法。
