169 research outputs found

    Spin echo without an external permanent magnetic field

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    The spin echo techniques aim at the elimination of the effect of a random magnetic field on the spin evolution. These techniques conventionally utlize the application of a permanent field which is much stronger than the random one. The strong field, however, may also modify the magnetic response of the medium containing the spins, thus altering their ``natural'' dynamics. We suggest an iterative scheme for generating a sequence of pulses which create an echo without an external permanent field. The approximation to the ideal echo improves with the sequence length

    Probing the ν=2/3\nu=2/3 fractional quantum Hall edge by momentum-resolved tunneling

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    The nature of the fractional quantum Hall state with filling factor ν=2/3\nu=2/3 and its edge modes continues to remain an open problem in low-dimensional condensed matter physics. Here, we suggest an experimental setting to probe the ν=2/3\nu=2/3 edge by tunnel-coupling it to a ν=1\nu=1 integer quantum Hall edge in another layer of a two-dimensional electron gas (2DEG). In this double-layer geometry, the momentum of tunneling electrons may be boosted by an auxiliary magnetic field parallel to the two planes of 2DEGs. We evaluate the current as a function of bias voltage and the boosting magnetic field. Its threshold behavior yields information about the spectral function of the ν=2/3\nu=2/3 edge, in particular about the nature of the chiral edge modes. Our theory accounts also for the effects of Coulomb interaction and disorder.Comment: 5 pages, 5 figures, and supplementary material (5 pages, 1 figure
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