  Chirality-induced spin selectivity (CISS) is an effect that has recently
attracted a great deal of attention in chiral chemistry and that remains to be
understood. In the CISS effect, electrons passing through chiral molecules
acquire a large degree of spin polarization. In this work we study the case of
atomically-thin chiral crystals created by van der Waals assembly. We show that
this effect can be spectacularly large in systems containing just two
monolayers, provided they are spin-orbit coupled. Its origin stems from the
combined effects of structural chirality and spin-flipping spin-orbit coupling.
We present detailed calculations for twisted homobilayer transition metal
dichalcogenides, showing that the chirality-induced spin polarization can be
giant, e.g. easily exceeding $50\%$ for ${\rm MoTe}_2$. Our results clearly
indicate that twisted quantum materials can operate as a fully tunable platform
for the study and control of the CISS effect in condensed matter physics and
chiral chemistry.
