  A new mechanism of bi-linear magnetoresistance (BMR) is studied theoretically
within the minimal model describing surface electronic states in topological
insulators (TIs). The BMR appears as a consequence of the second-order response
to electric field, and depends linearly on both electric field (current) and
magnetic field. The mechanism is based on the interplay of current-induced spin
polarization and scattering processes due to peculiar spin-orbit defects. The
proposed mechanism is compared to that based on a Fermi surface warping, and is
shown to be dominant at lower Fermi energies. We provide a consistent
theoretical approach based on the Green function formalism and show that the
magnetic field dependent relaxation processes in the presence of
non-equilibrium current-induced spin polarization give rise to the BMR.
