  The bistability of charge polarization in ferroelectric materials has long
been the basis of ferroelectric devices. However, the ferroelectricity tends to
be vanishing as the thickness of materials is reduced to a few nanometers or
thinner due to the depolarization field. Instead, they show a paraelectric or
an antiferroelectric ordering in the ultra-thin limit, which is unfavorable for
their applications in devices. Here we uncover polarization multistates in thin
films of van der Waals materials, in which the individual monolayers have an
antiferroelectric ordering with out-of-plane polarizations. This property
results from a unique combination of the polarization and layer degrees of
freedom. Using first-principles calculations, we demonstrate that bilayers and
trilayers of the CuInP$_2$S$_6$ family possess quintuple and septuple
polarization states., respectively. Our climbing image nudged elastic band
calculations for the bilayers and trilayers of CuInP$_2$S$_6$ and
CuCrP$_2$S$_6$ further show that the states can be transformed into each other
under appropriate external electric fields, for which a unique layer-selective
half-layer-by-half-layer flipping mechanism governs the transformings. Our
study opens up a door to design unusual polarization states using intrinsic
degrees of freedom of layered antiferroelectrics for the next-generation
ferroelectric devices that go beyond the bistability paradigm.
