Study On The Heat Generation In A Quantum Dot Coupled To Ferromagnetic Lead

In this paper, we carried out theoretical investigations on the heat generation in a quantum dot coupled to two electrodes in the framework of nonequilibrium Green’s function theory. This study can provide some valuable theoretical model for designing new nanoscale quantum devices with optimal properties.In chapter 1, we introduce some basic knowledge of mesoscopic system and the main theoretical method used in this thesis, i.e., nonequilibrium Green’s function technique. Besides, we also illuminate background and significance of the research on heat generation in quantum dot.In chapter 2, we study the properties of the heat flow generated by electric current in a quantum dot molecule sandwiched between two ferromagnetic leads. We find that when the leads’ magnetic moments are in parallel configuration, the total heat generation is independent on the leads’ spin-polarization regardless of the magnitude of the intradot Coulomb interaction. In the antiparallel configuration, however, the influences of the leads’ ferromagnetism on the heat generation are quite different from those on the electric current. Under the conditions of weak intradot Coulomb interaction and small bias voltage, the heat generation is monotonously suppressed by increasing leads’ spin-polarization. On the contrary, the heat generation shows non-monotonous behavior due to the electron-phonon interaction and the spin accumulation induced on the dot.In chapter 3, we investigate heat transport through a quantum dot coupled to one ferromagnetic lead and one normal metal lead. We find that due to the Coulomb blockade effect, the heat generation non-monotonously depend on the lead’s spin-polarization in the whole bias voltage regime. When the left lead’s spin-polarization is fixed, the spin polarization of the heat generation in positive biases is larger than that under negative biases. The current polarization is analogous to the tendency of the heat generation.In chapter 4, Electric-current-induced heat generation in an interacting single-level quantum dot connected to ferromagnetic leads with noncollinear magnetizations is theoretically investigated. We find that the magnitude of the heat generation is almost monotonously enhanced as the angle between the leads’ magnetic moments is varied from zero to?, while the magnitude of the electric current is continuously suppressed. Moreover, the properties of the heat generation depend on the lead’s spin polarization rate in different ways when the angle is varied. If at least one of the leads’ spin polarization rate approaches to unit, the spin-valve effect of the heat generation is identical to that of the electric current. As compared to the current, the heat generation is more sensitive to the system’s asymmetry when one of the electrodes is half-metallic in noncollinear configurations.Chapter 5 is the conclusion of the whole paper.