1 Anisotropic magnetoresistance in topological insulator Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 /CoFe heterostructures B. Xia 1 , P. Ren 1 , Azat Sulaev 1 , Z.P. Li 2 , P. Liu 1 , Z.L. Dong 2 , and L. Wang 1* 1. School of Physical and Mathematical Science, Nanyang Technological University, Singapore, 637371 2. School of Materials Science and Engineering, Nanyang Technological University, Singapore, 638798 Topological insulator is composed of an insulating bulk state and time reversal symmetry protected two-dimensional surface states. One of the characteristics of the surface states is the locking between electron momentum and spin orientation. Here, we report a novel in-plane anisotropic magnetoresistance in topological insulator Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 /CoFe heterostructures. To explain the novel effect, we propose that the Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 /CoFe heterostructure forms a spin-valve or Giant magnetoresistance device due to spin-momentum locking. The novel in-plane anisotropic magnetoresistance can be explained as a Giant magnetoresistance effect of the Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 /CoFe heterostructures. *Corresponding author: Lan Wang, Email: wanglan@ntu.edu.sg