169 research outputs found
Spin echo without an external permanent magnetic field
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 fractional quantum Hall edge by momentum-resolved tunneling
The nature of the fractional quantum Hall state with filling factor
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
edge by tunnel-coupling it to a 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 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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