Study On The Spin-Related Thermoelectric Effect In Semiconductor Quantum Dot

Thermoelectric devices has been well known and applied. With the development ofscience and technologies, how to further raise thermoelectric device’s efficiencybecome the focus of research.In the first chapter of this dissertation, we first simply describes the thermoelectriceffect in bulk materials, and then introduced the thermoelectric effect in nano-scalematerials and quantum dots, laying a foundation for the following parts.Chapter2devotes to the study of linear thermoelectric effect in a system composedof semiconductor quantum dot under the conditions of infinite small electric bias andtemperature difference. The thermoelectric quantities including electric conductance,thermal conductance, Seebeck coefficient and the figure of merit are calculated with thehelp of non-equilibrium Green’s function method. when the quantum dot is coupled toexternal ferromagnetic leads, moving electrons will become spin-polarized, imposingdistinct influence on the above physical quantities. This indicates a way of adjustingthermoelectric devices and the working conditions based on the electron spin degree offreedom.Chapter3devotes to the study of thermospin effect in a single quantum dotcoupled to ferromagnetic electrodes in the presence of Coulomb interaction. It is foundthat by optimizing the Coulomb interaction strength, the spin figure of merit can besignificantly enhanced. When the magnetic moments of the two electrodes are arrangedin parallel configuration, the magnitude of the spin figure of merit can be larger than1under certain conditions, which can be used in real design of thermal spintronics. Whilethe magnetic moments of the two electrodes are antiparallel to each other, the electronconductances of different spin-orientational are the same, and then the spin figure ofmerit is zero.Chapter4devotes to the study of thermoelectric effect in a small quantum dot witha magnetic impurity in the Coulomb blockade regime. The electrical conductance,thermal conductance, thermopower, and the thermoelectric figure of merit are calculatedby the Green’s function method. It is found that the peaks in the electrical conductanceare split by the exchange coupling between the electrons passing through the dot and themagnetic impurity, accompanied by the decrease in the peaks’ height. As a result of it,the resonances in the thermoelectric quantities are all split, opening some new working regions. Despite the significant reduction in the peaks’ height of the electricalconductance induced by the exchange coupling, the values of the figure of merit and thethermopower can be as large as those in the case of zero exchange coupling. We alsofind that the magnitude of the figure of merit can be enhanced by adjusting the left-rightasymmetry of the electrode-dot coupling or optimizing the system’s temperature.