  It is interesting to note that most black holes are born very slowly
rotating. We investigate scalarization of slowly rotating black holes in the
Einstein-scalar-Chern-Simons (EsCS) theory. In the slow rotation approximation,
the CS term takes a linear form of rotation parameter $a$ which determines the
tachyonic instability. The tachyonic instability for slowly rotating black
holes represents the onset of spontaneous scalarization. It is shown that the
slowly rotating black holes are unstable against a spherically symmetric
scalar-mode perturbation for positive coupling $\alpha$, whereas these black
holes are unstable for negative coupling without any $a$-bound.
