Coulomb Blockade Oscillations of Conductance in Quantum Dots
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Date
2018-12-04
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Addis Ababa University
Abstract
In this thesis, we studied the Coulomb blockade oscillations of conductance through
quantum dots. Quantum dots provide a new challenge to theoretical calculations for
their properties using many body methods. We consider a quantum dot, which is weakly
coupled by tunneling barriers to two electron reservoirs. Using the constant interaction
model between the charge carriers have calculated the conductance G of the quantum
dot is defined as G = I
V , in the limit V ! 0. We have shown the effect of the charging
and thermal energy, and level spacing on the conductance. Since transport through
quantum dot proceeds by tunneling through its discrete electronic states, it will be clear
that for a small V a net current can flow only for certain values of the gate voltage (if
_E >> kBT). We found an analytical expression for the conductance of a single electron
transistor in the regime when temperature, level spacing, and charging energy of a dot
are all of the same order.
In addition, we consider the model of equidistant energy levels in a dot in the sequential
tunneling approximation. For _ = 0.3, the normalized conductance is highly
oscillating with the largest amplitude and the normalized conductance becomes less oscillatory
as _ increases and in our case the least oscillation occurs for _ = 0.8 which is
consistent with the fact that the conductance becomes constant at high temperature.
To carried out the study we used a thermal energy for different level of spacing energy.
In this work we have done the numerical computation using fortran program and
plotted the result using gnuplot. We also studied the Coulomb blockade oscillations
of conductance at high and low temperatures using the variation of level spacing and
thermal energy. At low temperature there are sharp Coulomb blockade peak and for
high temperatures kBT >> Ec, _E, Coulomb blockade is lifted and small oscillations of
the conductance can be observed.
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Keywords
Coulomb Blockade, Oscillation, Conductance in Quantum Dots