  We reported the first spin potentiometric measurement to electrically detect
spin polarization arising from spin-momentum locking in topological insulator
(TI) surface states using ferromagnet/tunnel barrier contacts [1]. This method
has been adopted to measure the current generated spin in other TI systems
[2-10], albeit with conflicting signs of the measured spin voltage
[1,2,4,6-10]. Tian et al. wish to use their model as presented in Ref. [4] to
determine the sign of the induced spin polarization, and thereby determine
whether the claims of various groups to have sampled the topologically
protected surface states in bulk TIs are correct. The central point of our
Reply is that the model as presented is incapable of doing so because it fails
to include separate physical contributions which independently effect the sign
of the spin polarization measured.
