Browsing by Author "Bacha, Adisu"

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    Coulomb Blockade Oscillations of Conductance in Quantum Dots
    (Addis Ababa University, 2018-12-04) Bacha, Adisu; Elfagd, Yitagesu (PhD)
    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.