  We propose a Babinet-invertible chiral metasurface for achieving dynamically
reversible and strong circular dichroism (CD). The proposed metasurface is
composed of VO$_2$-metal hybrid structure, and when VO$_2$ transits between the
dielectric state and the metallic state, the metasurface unit cell switches
between complementary structures that are designed according to the Babinet
principle. This leads to a large and reversible CD tuning range between $\pm
0.5$ at 0.97~THz, which is larger than the literature. We attribute the CD
effect to extrinsic chirality of the proposed metasurface. We envision that the
Babinet-invertible chiral metasurface proposed here will advance the
engineering of active and tunable chiro-optical devices and promote their
applications.
