  Chiral phonons have attracted increasing attention, as they play important
roles in many different systems and processes. However, a method to control
phonon chirality by external fields is still lacking. Here, we propose that in
displacement-type ferroelectric materials, an external electric field can
reverse the chirality of chiral phonons via ferroelectric switching. Using
first-principles calculations, we demonstrate this point in the well known
two-dimensional ferroelectric In$_2$Se$_3$. This reversal may lead to a number
of electrically switchable phenomena, such as chiral phonon induced
magnetization, phonon Hall effect, and possible interface phonon modes at
ferroelectric domain boundaries. Our work offers a new way to control chiral
phonons, which could be useful for the design of thermal or information devices
based on them.
