Study On Modulation Of Spin And Valley Diode Effect And Thermal Transport In Two-dimensional Systems

The two intrinsic degrees of freedom of electrons,charge and spin,are the basic stones of modern electronic information technology.In the past century,the traditional semiconductor microelectronics dominated by the charge degree of freedom of electrons has got fast development,At the end of last century,the discovery of giant magnetoresistence effect enriches people's understanding of the spin degree of freedom of electrons,and promotes the development and application of magnetic storage,magnetic sensing and other technologies.Since 2004,a series of two-dimensional new materials such as graphene,silene,germanene,transition metal dichalcogenides have been successfully fabricated,another electron degree of freedom called "valley" has also aroused great research interest,specifically for the coupled property of valley and spin.This provides a new operation method mediated by valley.This thesis focuses on the study of the realization approach and physical mechanism associated with valley in two-dimensional magnetic systems.Our research provides physical basis for designing two-dimensional spintronic devices with high performance,low dissipation and easily integration.In Chaper one,we mainly overview the development history,physical phenomena and mechanism,from traditional charge diodes to spin valves,spin diodes,and then to valley Hall devices and valley diodes.In Chapter two,we introduce the basic concepts and theoretical methods needed in our research.In Chapter three,we discuss how to realize the spin diode effect based on the concept of valley.Our theoretical model is based on a pn junction constructed from monolayer molybdenum disulfide.The magnetism is induced by magnetic proximity effect through contacting molybdenum disulfide with ferromagnetic insulators.P-type and N-type impurities locate on the left and right sides of pn junction and are formed by free diffusion of carriers.At the same time,the effective modulation can be realized by adjusting the chemical potential after N-type impurity doping,P-type impurity doping chemical potential and longitudinal bias voltage,and the carriers can be limited within two specific regions to achieve unidirectional conductivity.This means,only the electrons from a single valley contribute to the current,and only one spin is forward conductive but backward cutoff,while the other spin is always cut off.Our further study indicates that the unipolar spin diode effect can be realized when the ferromagnetic exchange field exists at lease one side of P region and N region.In Chapter four,we discuss the novel thermoelectric effects in magnetic solid-state electronic devices.We focus on the novel physical phenomena such as Seebeck effect and Nernst effect related to electron charge,spin and valley,and their modulation mechanism,and discuss their development,design and possible applications in new thermoelectric components in the near future.Finally,we give the conclusion and prospect as well as acknowledgement.