The quantum spin Hall effect

In a two-dimensional system the quantum spin Hall effect (QSHE) state is characterized by an insulating bulk and two counter-propagating helical edge states. These edge channels are protected by time reversal symmetry and spin currents propagate without dissipation. It was shown that HgTe-based quantum well structures are the most suitable candidates for its experimental realization. Here, the experimental requirements are discussed which lead to the observation of quantized edge channel transport which is one of the main signatures of the QSHE. Experiments will be presented which demonstrate the stability of the quantized conductance and its nonlocal character. Furthermore, evidence for the spin polarization of the QSHE edge channels is shown in an all-electrical measurement which demonstrates the potential of the QSHE for spin injection and detection applications in spintronics. (C) 2011 American Institute of Physics. [doi:10.1063/1.3577612]