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We study the edge-channel transport at quantum Hall (QH) transition regions for a high-mobility Si / Si Ge QH conductor by measuring nonlocal resistance (RNL). The RNL as a function of magnetic field changes drastically after Landau-level crossings. The features of the RNL depend on the spin configuration between the innermost edge channel and the bulk state: the RNL appears only when the relevant edge-bulk states have opposite spin orientations. Also, an origin of the spin-dependent resistivity [Phys. Rev. Lett. 94, 176402 (2005)] at QH transition regions is discussed in terms of the spin-dependent inter-edge-bulk scattering. |
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The authors have developed a method for electrical polarization of nuclear spins in quantum Hall systems. In a breakdown regime of odd-integer quantum Hall effect (QHE), excitation of electrons to the upper Landau subband with opposite spin polarity dynamically polarizes nuclear spins through the hyperfine interaction. The polarized nuclear spins in turn accelerate the QHE breakdown, leading to hysteretic voltage-current characteristics of the quantum Hall conductor. |