531 research outputs found
Charge and spin addition energies of one dimensional quantumn dot
We derive the effective action for a one dimensional electron island formed
between a double barrier in a single channel quantum wire including the
electron spin. Current and energy addition terms corresponding to charge and
spin are identified. The influence of the range and the strength of the
electron interaction and other system parameters on the charge and spin
addition energies, and on the excitation spectra of the modes confined within
the island is studied. We find by comparison with experiment that spin
excitations in addition to non-zero range of the interaction and inhomogeneity
effects are important for understanding the electron transport through one
dimensional quantum islands in cleaved-edge-overgrowth systems.Comment: 11 pages, 3 figures, to be published in Physical Review
Coherent Transport through a Quantum Dot Embedded in an Aharonov-Bohm Ring
We study the coherent transport in multi-terminal mesoscopic Aharonov-Bohm
ring with a quantum dot embedded in an arm. Employing the Friedel sum rule for
the effective single-particle levels in the quantum dot, we explain some
anomalous features which have been observed in the experiment. We attribute
these anomalies to the result of nontrivial quantum interference of the quantum
dot with the attached ring. Further, we propose a new feature of conductance
oscillations which can be a test for the validity of our model.Comment: 4 pages Revtex, 4 Postscript figures, accepted for publication in
Phys. Rev.
Inhomogeneous Nuclear Spin Flips
We discuss a feedback mechanism between electronic states in a double quantum
dot and the underlying nuclear spin bath. We analyze two pumping cycles for
which this feedback provides a force for the Overhauser fields of the two dots
to either equilibrate or diverge. Which of these effects is favored depends on
the g-factor and Overhauser coupling constant A of the material. The strength
of the effect increases with A/V_x, where V_x is the exchange matrix element,
and also increases as the external magnetic field B_{ext} decreases.Comment: 5 pages, 4 figures (jpg
Channel Interference in a Quasi Ballistic Aharonov-Bohm Experiment
New experiments are presented on the transmission of electron waves through a
2DEG (2 dimensional electron gas) ring with a gate on top of one of the
branches. Magnetoconductance oscillations are observed, and the phase of the
Aharanov-Bohm signal alternates between 0 and pi as the gate voltage is
scanned. A Fourier transform of the data reveals a dominant period in the
voltage which corresponds to the energy spacing between successive transverse
modes.A theoretical model including random phase shifts between successive
modes reproduces the essential features of the experiment.Comment: 4 pages, 6 Postscript figures, TEX, submitted to Physical Review
Letter
Topological blockade and measurement of topological charge
The fractionally charged quasiparticles appearing in the 5/2 fractional
quantum Hall plateau are predicted to have an extra non-local degree of
freedom, known as topological charge. We show how this topological charge can
block the tunnelling of these particles, and how such 'topological blockade'
can be used to readout their topological charge. We argue that the short time
scale required for this measurement is favorable for the detection of the
non-Abelian anyonic statistics of the quasiparticles. We also show how
topological blockade can be used to measure braiding statistics, and to couple
a topological qubit with a conventional one.Comment: Published version: one additional paragraph (on the 331 state); Figs.
1 and 4 modified; Ref. 46 adde
Features of spin-charge separation in the equilibrium conductance through finite rings
We calculate the conductance through rings with few sites described by
the model, threaded by a magnetic flux and weakly coupled to
conducting leads at two arbitrary sites. The model can describe a circular
array of quantum dots with large charging energy in comparison with the
nearest-neighbor hopping . We determine analytically the particular values
of for which a depression of the transmittance is expected as a
consequence of spin-charge separation. We show numerically that the equilibrium
conductance at zero temperature is depressed at those particular values of
for most systems, in particular at half filling, which might be easier
to realize experimentally.Comment: 8 pages, 7 figure
Spin-charge separation in strongly interacting finite ladder rings
We study the conductance through Aharonov-Bohm finite ladder rings with
strongly interacting electrons, modelled by the prototypical t-J model. For a
wide range of parameters we observe characteristic dips in the conductance as a
function of magnetic flux, predicted so far only in chains which are a
signature of spin and charge separation. These results open the possibility of
observing this peculiar many-body phenomenon in anisotropic ladder systems and
in real nanoscopic devices.Comment: 4 pages, 6 figure
Spatial structure of an incompressible Quantum Hall strip
The incompressible Quantum Hall strip is sensitive to charging of localized
states in the cyclotron gap. We study the effect of localized states by a
density functional approach and find electron density and the strip width as a
function of the density of states in the gap. Another important effect is
electron exchange. By using a model density functional which accounts for
negative compressibility of the QH state, we find electron density around the
strip. At large exchange, the density profile becomes nonmonotonic, indicating
formation of a 1D Wigner crystal at the strip edge. Both effects, localized
states and exchange, lead to a substantial increase of the strip width.Comment: 6 LaTeX pages, 2 postscript figures, to be published in EP2DS
proceeding
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