  Searching for topological insulators in solids is one of the main issues of
modern condensed matter physics since robust gapless edge or surface states of
the topological insulators can be used as building blocks of next-generation
devices. Enhancing spin-orbit couplings is a promising way to realize
topological insulators in solids, whereas the amplitude of the spin-orbit
couplings is not sufficiently large in most materials. Here we show a way to
realize a topological state characterized by the quantized Zak phase, termed
the Zak insulator, with spin-polarized edges in organic antiferromagnetic Mott
insulators without relying on the spin-orbit coupling. The obtained Zak
insulator can have a large charge gap compared to the conventional topological
insulators, since Coulomb interactions mainly govern the amplitude of the
charge gap in the antiferromagnetic Mott insulators. Besides the mean-field
analysis, we demonstrate that the Zak insulator survives against electron
correlation effects by calculating the many-body Zak phase. Our finding
provides an unprecedented way to realize a topological state in strongly
correlated electron systems.
