دراسة نظرية لفحص نقل الالكترون خلال نقطتين كميتن مقترنتين == Theoretical Study to Investigate the Electron Transport Through Double Coupled Quantum Dots
Author name:
محمد عبد الزهرة نجدي
Supervisor name:
هيفاء عبد النبي جاسم
General topic:
Physics
Specific topic:
Physics
Degree:
Master
University:
University Of Basrah - College Of Science
Language:
Arabic
University location:
Basrah
First pages:
26T1689 - p.pdf
Abstract:
In this study, a model calculation is introduced for the electron transportthrough a system consists of two quantum dots coupled serially, embeddedbetween two nonmagnetic leads (source and drain), due to the importance ofthis kind of systems in many academic and experimental applications.In our treatment, the time independent Anderson - Newns Hamiltonian modelis considered as a basis to study the system dynamics and then to derive spindependentanalytical formula to calculate the occupation numbers of thequantum dots energy levels, the corresponding quantum dots energy levelsand the molecular virtual energy levels, as a function of bias voltage .These relations are solved self - consistently, which are all employed tocalculate the tunneling current. The differential conductance is calculatednumerically by using finite differences method.And as the efficiency of electron transport through coupled quantum dotsdepends on the system parameters such as the energy levels position of eachquantum dot, the Coulomb repulsion energy on each quantum dot, theeffective exchange energy, the tunneling coupling between the dots and leadsand the coupling energy between the two quantum dots, all these parametersare studied and investigated in details and the role of all these parameters inthe tunneling current and the differential conductance calculations ispresented. also our treatment is applied to two kinds of systems, when thequantum dots are symmetric and when they are asymmetric depending on ourchoice for the over mentioned parameters. Our treatment is utilized to studythe following : 1 - - - Two regimes are studied, the first is the strong coupling regime and thesecond is the weak coupling regime.2 - - - The role of the spin exchange interaction in determining the type ofinteraction (if it is attractive or repulsive) between the quantum dots.3 - - - The role of the spin exchange interaction between the quantum dots indetermining the coulomb blockade in the strong coupling regime.And according to our calculations, we conclude that at the strong couplingand when neglecting the effective exchange interaction, one can determinethe bias voltage values that correspond to the maximum values of thedifferential conductance which is equal to the value of the couplinginteraction between the quantum dots. And the maximum and minimumvalues in the differential conductance curve are changed when the quantumdots energy levels are lying below the energy reference. Also, ourcalculations that concern to the effective exchange interaction make it sure that our results can be utilized to study the electronics that related to the coupled quantum dots. Our calculations that related to the Coulomb blockade make it sure that one can use the quantum dots molecule as an electronic switch. Our calculations that concern to the gate voltage effect investigation in the case of equilibrium can be employed in the detection about the type of coupling with the environmental which effects directly in determining the rates of electron tunneling from the left lead to the active region and then to the right lead.
