  Motivated by a recent experiment (Sanchez-Yamagishi et.al, arXiv:1602.06815)
reporting evidence of helical spin-polarized edge states in layer-biased
twisted bilayer graphene under a magnetic flux, we study the possibility of
stabilising a Quantum Spin Hall (QSH) phase in such a system, without Zeeman or
spin-orbit couplings, and with a QSH gap induced instead by electronic
interactions. We analyse how magnetic flux, electric field, interlayer rotation
angle, and interactions (treated at a mean field level) combine to produce a
pseudo-QSH with broken time-reversal symmetry, and spin-polarized helical edge
states. The effect is a consequence of a robust interaction-induced
ferrimagnetic ordering of the Quantum Hall ground state under an interlayer
bias, provided the two rotated layers are effectively decoupled at low
energies. We discuss in detail the electronic structure, and the constraints on
system parameters, such as the angle, interactions and magnetic flux, required
to reach the pseudo-QSH phase. We find, in particular, that purely local
electronic interactions are not sufficient to account for the experimental
observations, which demand at least nearest-neighbour interactions to be
included.
