Spin dephasing and 'hot spins'

摘要

At this summer school, I have tried to describe a general approach to quantum transport problems based on the Non-Equilibrium Green Function (NEGF) method following the simple heuristic approach described in [1]. I will not repeat this treatment here. Instead I will use this article to draw attention to a core issue in quantum transport and how it is modeled within the NEGF method. Specifically, I will discuss what constitutes a dephasing process and how the standard descriptions may need to be extended to include what I will call "hot spin" effects. These involve a number of subtle issues that tend to get hidden in a purely formal description. So I have chosen instead to illustrate the concepts using a concrete device, which is specially engineered to enhance its sensitivity to spin dephasing and hot-spin effects. I will call this device a spin-charge transducer for it converts spin excitations into charge currents and vice versa. It is closely related to the well-known spin-valve device but to my knowledge the spin-charge transducer described here has not been discussed before. I believe devices of this type deserve a serious look from an applied point of view, but that is a different story —here I will use it purely as a pedagogical tool.