Spin Seebeck Effiect In Ring-shape Triple-quantum-dot Systems

With the development of spintronics,the spin thermoelectric effect has received much attention in the past two decades.The central issue in spintronics is the control of electron spins by electrical bias,whereas in spin thermoelectric effect,the method of spin control is mainly the thermal bias,i.e.,a temperature gradient applied between different ends of the system.It is therefore considered to be a combination of spintronics and thermoelectricity.In this thesis we study the spin Seebeck effect in a triple-quantum-dot systems with two different configurations.We focus on the function of the spin-dependent inter-dot couplings,which can be realized by applying a static magnetic on the junctions between the dots,on enhancing the thermoelectric efficiency and the thermopower value.The present systems are modeled by the multi-impurity Anderson Hamilton,and electron transmission probability is calculated by using the equation of motion technique within the framework of nonequilibrium Keldysh green function,our main results include:(i)In the triple-dot-ring coupled to ferromagnetic leads,the collaboration of the magnetism of the leads and the spin-dependent interdot couplings result in large spin thermopower and spin figure of merit.The functions of the destructive quantum interference are quite distinct.Moreover,the signs of the spin thermopower can be adjusted by changing the leads ferromagnetism and the spin-dependent interdot coupling.(ii)In the structure with only one of the three dots is coupled to normal metal leads and the dots are serially connected,obvious 100% spin polarized and pure thermopower emerge under the conditions of large enough interdot coupling spin polarization with strong dot-dot couplings.If the dots are weakly coupled,giant 100% spin polarized spin thermopower emerge under small interdot spin polarization.When the dots are connected in a ring,the thermopower is anti-asymmetric and develops peak aournd the Fano antiresonant state.By changing the spin polarization of the interdot coupling,spin-up and spin-down thermopower move to opposite directions in dot energy space and induces 100% spin-polarized and pure spin thermopower.(iii)In the presence of both spin-dependent interdot couping and magnetic flux penetrating through the system,their combined actions lead to not only the enhancement of the 100% spin-polarized and pure spin thermopower,but also their sign change.Now the value of the spin thermopower is sensitive to the dot level's detuning and the manipulation methods of the spin thermopower become more rich.