Dr. Xingyue Peng
UCD
时间：2014-9-1（星期一）上午10：30
地点：唐仲英楼A-107(2)
摘要：We introduce a fundamentally new spin generation mechanism in 3-dimensional topological insulators (3D TIs), which originates from the topologically non-trivial band structure. Unlike the usual case where spin generation is believed to happen independently on the top and bottom surfaces of the 3D TI, in this mechanism the insulating yet topologically non-trivial bulk plays an essential role in transporting spins. A rigorous calculation followed by a comprehensive physical picture clearly illustrates this mechanism. Comparison to other 2-dimensional (2D) systems including graphene and 2D electron gas (2DEG) with Rashba-like splitting further clarifies the importance of non-trivial band topology. When the impurity density is high, as in practical 3D TI materials, the spin relaxation process is suppressed by frequent nonmagnetic scatterings through the Dyakonov-Perel mechanism and the resultant spin accumulation is enhanced. The enhanced spin accumulation is manifested in the large conductivity residue when the Fermi level is tuned to the Dirac point, which has often been observed in experiment but not satisfactorily explained before this work. The spin generation mechanism presented in this work is not only fundamentally important but also provides a new approach for enhancing spin polarization in novel spintronic devices by increasing nonmagnetic impurity density.