Study On Spin Transport Phenomena In Several Low–Dimensional Quantum Systems Under The External Field

With the continuous advancement of information technology,emerging nanoscience and engineering,spintronics has grown into a vast field spanning basic science,engineering design and industrial production.Not only has the great scientific value,also has the enormous commercial application.Exploring the new spin material systems,as well as corresponding spin information processing frame have become the key in new round high-tech competition.In this paper,the spin dependent transport properties of the typical low-dimensional quantum systems—zero-dimensional quantum dot system,and the novel monomolecular two-dimensional material(silicene,germanene,stanene,molybdenum disulfide)under the control of the external field are studied.The semiconductor quantum dot systems under Terahertz irradiation present rich and unique spin thermoelectric properties,and the quantum states in two-dimensional materials can be regulated by the external field,providing a theoretical possibility for the realization of new spin devices.The spin thermoelectric transport of In As quantum dots under magnetic field and terahertz radiation is discussed.In the case of symmetric terahertz radiation,the spin figure of merit shows much more dependence on temperature and magnetic field that the charge figure of merit.In asymmetric THz irradiation,we can change the direction of thermal current by adjusting the frequency asymmetry rate of THz irradiation,which induces the cooling effect.It is worth noting that we have achieved a complete externally driven asymmetry,which does not involve the parameters and properties of the system,and is easy to control and realize in practical applications.Fano resonance and thermoelectric transport of A-B ring quantum dot system under terahertz radiation are studied.Numerical simulation results show that the current presents a symmetrical line under asymmetric terahertz irradiation by Fano effect together with the photo-electron pump effect.In addition,with the increase of the terahertz irradiation intensity or frequency,the system can obtain the restricted power zone near the main Coulomb peak,and the output power value at the side peak position is improved to a certain extent.We theoretically propose a spin field effect transistor based on germanene and stanene nanoribbons under the control of both external light field and electric field.When the field intensity of light field and electric field is greater than or equal to the coupling strength of spin-orbit coupling,the phase transition occurs at the edge state of the nanoribbons,and the spin filtering effect can be realized.More importantly,we can achieve the switching effect by applying different optical fields with different curl in different regions,and realizing the spin field effect transistor based on the based on germanene and stanene nanoribbons.The spin transport properties of normal/ferromagnetic/normal monolayer Zigzag molybdenum disulfide nanoribbon junction under the same strength of exchange and electric fields are studied by using the three-band tight-binding model combined with non-equilibrium Green's function method.The results show that the conductance of the spin down is independent on the applied external fields and presents quantization platform effect.In addition,enlarging the action region of the external field increasing the overall temperature of the system will greatly weaken the trend of the spin-down conductance oscillation and greatly expand the effective energy range of the spin filtering effect.