  Material systems that exhibit tunable spin-selective conductivity are key
components of spintronic technologies. Here we demonstrate a novel type of
spin-selective transport, based on the unusual Landau level (LL) sequence
observed in bilayer WSe$_2$ under large applied magnetic fields. We find that
the conductivity depends strongly on the relative iso-spin ordering between
conducting electrons in a partially filled LL and the localized electrons of
lower energy filled LLs, with conductivity observed to be almost completely
suppressed when the spin-ratio and field-tuned Coulomb energy exceed a critical
threshold. Switching between "on/off" states is achievable through either
modulation of the external magnetic or electric fields, with many-body
interaction driving a collective switching mechanism. In contrast to
magnetoresistive heterostructures, this system achieves electrically tunable
spin filtering within a single material, driven by interaction between free and
localized spins residing in energy-separated spin/valley polarized bands.
Similar spin-selective conductivity may be realizable in multi-flat band
systems at zero magnetic field.
