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In this talk, I will discuss some of our recent results on the quantum spin Hall effect in HgTe-based two-dimensional topological insulators. In the first part, I will show that the conductance quantization due to the quantum spin Hall effect can be observed even in the presence of magnetic impurities. Our experiments on (Hg,Mn)Te quantum wells with an inverted band structure reveal that the quantum spin Hall quantization is observed only at low temperatures (T < 400 mK), where Kondo screening of the magnetic impurities suppresses backscattering. The second part of the talk will focus on understanding the fluctuations in the quantized spin Hall conductance that has been observed in almost all realizations of the quantum spin Hall effect - including the first paper in 2007. To examine these fluctuations, we fabricate high-quality quantum spin Hall microstructures using a carefully optimized wet-etching process. We perform temperature and gate-dependent measurements in the regime of quantized conductance. The fluctuations in conductance show a characteristic temperature dependence that is related to Kondo interactions of helical edge channels with small puddles. These charge puddles - acting as Kondo correlated quantum dots due to small dimensions - arise due to fluctuations in the potential landscape in narrow gap semiconductors.

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Saquib Shamin/ University of Würzburg
room 0.03
Contact: Erwann Boquillon