139 research outputs found
Ultralow Temperature Studies of Nanometer Size Semiconductor Devices
Contains report on one research project.Joint Services Electronics Program (Contract DAAL03-86-K-0002)Joint Services Electronics Program (Contract DAAL03-89-C-0001
Ultralow-Temperature Measurements of Submicron Devices
Contains research summary.Joint Services Electronics Program (Contract DAALO03-86-K-0002
Ultralow-Temperature Measurements of Submicron Devices Nanometer-Scale Semiconductor Devices
Contains project goals.Joint Services Electronics Program (Contract DAALO3-86-K-0002
Wigner Crystal in One Dimension
A one--dimensional gas of electrons interacting with long--range Coulomb
forces () is investigated. The excitation spectrum consists
of separate collective charge and spin modes, with the charge excitation
energies in agreement with RPA calculations. For arbitrarily weak Coulomb
repulsion density correlations at wavevector decay extremely slowly and
are best described as those of a one--dimensional Wigner crystal. Pinning of
the Wigner crystal then leads to the nonlinear transport properties
characteristic of CDW. The results allow a consistent interpretation of the
plasmon and spin excitations observed in one--dimensional semiconductor
structures, and suggest an interpretation of some of the observed features in
terms of ``spinons''. A possible explanation for nonlinear transport phenomena
is given.Comment: 10 pages, RevTe
Kondo resonance effect on persistent currents through a quantum dot in a mesoscopic ring
The persistent current through a quantum dot inserted in a mesoscopic ring of
length L is studied. A cluster representing the dot and its vicinity is exactly
diagonalized and embedded into the rest of the ring. The Kondo resonance
provides a new channel for the current to flow. It is shown that due to scaling
properties, the persistent current at the Kondo regime is enhanced relative to
the current flowing either when the dot is at resonance or along a perfect ring
of same length. In the Kondo regime the current scales as , unlike
the scaling of a perfect ring. We discuss the possibility of detection
of the Kondo effect by means of a persistent current measurement.Comment: 11 pages, 3 Postscript figure
Transport properties of a quantum wire in the presence of impurities and long-range Coulomb forces
One-dimensional electron systems interacting with long-range Coulomb forces
(quantum wires) show a Wigner crystal structure. We investigate in this paper
the transport properties of such a Wigner crystal in the presence of
impurities. Contrary to what happens when only short-range interactions are
included, the system is dominated by scattering on the impurities.
There are two important length scales in such a problem: one is the pinning
length above which the (quasi-)long-range order of the Wigner crystal is
destroyed by disorder. The other length is the length below which
Coulomb interactions are not important and the system is behaving as a standard
Luttinger liquid with short-range interactions. We obtain the frequency and
temperature dependence of the conductivity. We show that such a system is very
similar to a classical charge density wave pinned by impurities, but with
important differences due to quantum fluctuations and long-range Coulomb
interactions. Finally we discuss our results in comparison with experimental
systems.Comment: 25 pages, RevTex3.
Ultralow Temperature Studies of Nanometer Size Semiconductor Devices
Contains a description on one research project.Joint Services Electronics Program DAAL03-89-C-000
Correlation and symmetry effects in transport through an artificial molecule
Spectral weights and current-voltage characteristics of an artificial
diatomic molecule are calculated, considering cases where the dots connected in
series are in general different. The spectral weights allow us to understand
the effects of correlations, their connection with selection rules for
transport, and the role of excited states in the experimental conductance
spectra of these coupled double dot systems (DDS). An extended Hubbard
Hamiltonian with varying interdot tunneling strength is used as a model,
incorporating quantum confinement in the DDS, interdot tunneling as well as
intra- and interdot Coulomb interactions. We find that interdot tunneling
values determine to a great extent the resulting eigenstates and corresponding
spectral weights. Details of the state correlations strongly suppress most of
the possible conduction channels, giving rise to effective selection rules for
conductance through the molecule. Most states are found to make insignificant
contributions to the total current for finite biases. We find also that the
symmetry of the structure is reflected in the I-V characteristics, and is in
qualitative agreement with experiment.Comment: 25 figure files - REVTEX - submitted to PR
Conductance and density of states as the Kramers-Kronig dispersion relation
By applying the Kramers-Kronig dispersion relation to the transmission
amplitude a direct connection of the conductance with the density of states is
given in quantum scattering systems connected to two one-channel leads.
Using this method we show that in the Fano resonance the peak position of the
density of states is generally different from the position of the corresponding
conductance peak, whereas in the Breit-Wigner resonance those peak positions
coincide.
The lineshapes of the density of states are well described by a Lorentz type
in the both resonances.
These results are verified by another approach using a specific form of the
scattering matrix to describe scattering resonances.Comment: 9 pages, 4 figure
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