Thermoelectric Transport Properties In Low-dimensional Systems

With the rapid development of nanotechnology,the device tends to the nanometer scale,which creat a powerful condition for the practical application of spintronics, valleytronics and spin caloritronics. Since graphene is found, the researchs on the two-dimensional electronic devices have received widespread attention. The study of the thermoelectric transport in low dimensional systems can be a theoretical basis for the application of two-dimensional electronic devices. In this paper, we focus on the thermoelectric transport in low dimensional systems, mainly including the thermoelectric transport phenomena in quantum dots and silicence junctions.In second chapter, we study thermoelectric effect through a quantum dot with a magnetic field. In the stationary case, we obtain a tunable pure spin current and highly spin-polarized current. A pure spin Seebeck coefficient is found. In the presence of microwave field, the spin and charge current can be controlled by the amplitude of microwave field. Due to the photo-assisted tunneling, the behavior of spin polarization becomes complicated. At zerogV, we can modulate both amplitude and direction of the spin current by the phase of microwave field.In third chapter, We have investigated the valley and spin resolved thermoelectric transport in ferrmagnetic silicence junctions. Due to the coupling between the valley and spin degree of the freedom, thermally induced pure valley and spin currents can be demonstrated. The magnitude and sign of these currents can be manipulated by adjusting the ferromagnetic exchange field and local external electric field, thus the currents are controllable. We also find fully valley and/or spin polarized current. Similar to the currents, owing to the band structure symmetry, tunable pure spin and/or valley thermopowers are generated.Whether in a quantum dot or in ferrmagnetic silicence junctions, the current and Seebeck coefficient we study are controllable, which not only has a high value for the future practical application of thermoelectric transport, but also opens up a new direction for the development of the low dimensional electronic devices.