94 research outputs found
Effects of surface forces and phonon dissipation in a three-terminal nano relay
We have performed a theoretical analysis of the operational characteristics
of a carbon-nanotube-based three-terminal nanorelay. We show that short range
and van der Waals forces have a significant impact on the characteristics of
the relay and introduce design constraints. We also investigate the effects of
dissipation due to phonon excitation in the drain contact, which changes the
switching time scales of the system, decreasing the longest time scale by two
orders of magnitude. We show that the nanorelay can be used as a memory element
and investigate the dynamics and properties of such a device
A Carbon Nanotube Based Nanorelay
We investigate the operational characteristics of a nanorelay based on a
conducting carbon nanotube placed on a terrace in a silicon substrate. The
nanorelay is a three terminal device that acts as a switch in the GHz regime.
Potential applications include logic devices, memory elements, pulse
generators, and current or voltage amplifiers.Comment: 4 pages, 3 figure
Many-body interactions in a quantum wire in the integer quantum Hall regime: suppression of exchange-enhanced g factor
The collapse of Hall gaps in the integer quantum Hall liquid in a quantum
wire is investigated. Motivated by recent experiment [Pallecchi et al. PRB 65,
125303 (2002)] previous approaches are extended to treat confinement effects
and the exchanged enhanced g-factor in quantum wires. Two scenarios for the
collapse of the state are discussed. In the first one the
state becomes unstable at , due to the exchange interaction and
correlation effects, coming from the edge-states screening. In the second
scenario, a transition to the state occurs at , with a
smaller effective channel width, caused by the redistribution of the charge
density. This effect turns the Hartree interaction essential in calculating the
total energy and changes drastically. In both scenarios, the
exchange enhanced g-factor is suppressed for magnetic fields lower than
. Phase diagrams for the Hall gap collapse are determined. The critical
fields, activation energy, and optical -factor obtained are compared with
experiments. Within the accuracy of the available data, the first scenario is
most probable to be realized.Comment: 11 pages, 10 figure
Interplay of Coulomb blockade and Aharonov-Bohm resonances in a Luttinger liquid
We consider a ring of strongly interacting electrons connected to two
external leads by tunnel junctions. By studying the positions of conductance
resonances as a function of gate voltage and magnetic flux the interaction
parameter can be determined experimentally. For a finite ring the minimum
conductance is strongly influenced by device geometry and electron-electron
interactions. In particular, if the tunnel junctions are close to one another
the interaction-related orthogonality catastrophe is suppressed and the valley
current is unexpectedly large.Comment: 10 page
Ensemble density-functional approach to charge-spin textures in inhomogeneous quantum Hall systems
We extend our ensemble density-functional approach to quantum Hall systems to include noncollinear spins to study charge-spin textures in inhomogeneous quantum Hall systems. We have studied the edge reconstruction in quantum dots at unit bulk filling factor and at 1/3 bulk filling factor as a function of the stiffness of an external confining potential. For soft enough edges, these systems reconstruct to a state in which the electron spins rotate gently as the edge is approached, with a nontrivial spin-charge texture at the edge of the system
Mechanical cat states in graphene resonators
We study the quantum dynamics of a symmetric nanomechanical graphene
resonator with degenerate flexural modes. Applying voltage pulses to two back
gates, flexural vibrations of the membrane can be selectively actuated and
manipulated. For graphene, nonlinear response becomes important already for
amplitudes comparable to the magnitude of zero point fluctuations. We show,
using analytical and numerical methods, that this allows for creation of
cat-like superpositions of coherent states as well as superpositions of
coherent cat-like non-product states.Comment: 4 pages, 3 figure
Parametric resonances in electrostatically interacting carbon nanotube arrays
We study, numerically and analytically, a model of a one-dimensional array of
carbon nanotube resonators in a two-terminal configuration. The system is
brought into resonance upon application of an AC-signal superimposed on a
DC-bias voltage. When the tubes in the array are close to each other,
electrostatic interactions between tubes become important for the array
dynamics. We show that both transverse and longitudinal parametric resonances
can be excited in addition to primary resonances. The intertube electrostatic
interactions couple modes in orthogonal directions and affect the mode
stability.Comment: 11 pages, 12 figures, RevTeX
Fractional Quantum Hall States in Narrow Channels
A model system is considered where two dimensional electrons are confined by
a harmonic potential in one direction, and are free in the other direction.
Ground state in strong magnetic fields is investigated through numerical
diagonalization of the Hamiltonian. It is shown that the fractional quantum
Hall states are realized even in the presence of the external potential under
suitable conditions, and a phase diagram is obtained.Comment: 8 pages, 2 figures (not included
Shot Noise and Full Counting Statistics from Non-equilibrium Plasmons in Luttinger-Liquid Junctions
We consider a quantum wire double junction system with each wire segment
described by a spinless Luttinger model, and study theoretically shot noise in
this system in the sequential tunneling regime. We find that the
non-equilibrium plasmonic excitations in the central wire segment give rise to
qualitatively different behavior compared to the case with equilibrium
plasmons. In particular, shot noise is greatly enhanced by them, and exceeds
the Poisson limit. We show that the enhancement can be explained by the
emergence of several current-carrying processes, and that the effect disappears
if the channels effectively collapse to one due to, {\em e.g.}, fast plasmon
relaxation processes.Comment: 9 pages; IOP Journal style; several changes in the tex
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